feat(ui): Add project theme selection to context menu with clean code refactoring

Implement per-project theme override capability in the Discord-like layout:
- Add theme submenu to project context menu with live preview
- Reuse existing theme constants and useThemePreview hook from sidebar
- Extract reusable ThemeButton and ThemeColumn components (DRY principle)
- Replace magic z-index values with named constants

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/components/layout/project-switcher/components/project-context-menu.tsx

@@ -1,9 +1,105 @@
-import { useEffect, useRef, useState } from 'react';
-import { Edit2, Trash2 } from 'lucide-react';
+import { useEffect, useRef, useState, memo } from 'react';
+import type { LucideIcon } from 'lucide-react';
+import { Edit2, Trash2, Palette, ChevronRight, Moon, Sun, Monitor } from 'lucide-react';
 import { cn } from '@/lib/utils';
-import { useAppStore } from '@/store/app-store';
+import { type ThemeMode, useAppStore } from '@/store/app-store';
 import { ConfirmDialog } from '@/components/ui/confirm-dialog';
 import type { Project } from '@/lib/electron';
+import { PROJECT_DARK_THEMES, PROJECT_LIGHT_THEMES } from '@/components/layout/sidebar/constants';
+import { useThemePreview } from '@/components/layout/sidebar/hooks';
+
+// Constants for z-index values
+const Z_INDEX = {
+  CONTEXT_MENU: 100,
+  THEME_SUBMENU: 101,
+} as const;
+
+// Theme option type from sidebar constants
+interface ThemeOption {
+  value: string;
+  label: string;
+  icon: LucideIcon;
+  color: string;
+}
+
+// Reusable theme button component to avoid duplication (DRY principle)
+interface ThemeButtonProps {
+  option: ThemeOption;
+  isSelected: boolean;
+  onPointerEnter: () => void;
+  onPointerLeave: (e: React.PointerEvent) => void;
+  onClick: () => void;
+}
+
+const ThemeButton = memo(function ThemeButton({
+  option,
+  isSelected,
+  onPointerEnter,
+  onPointerLeave,
+  onClick,
+}: ThemeButtonProps) {
+  const Icon = option.icon;
+  return (
+    <button
+      onPointerEnter={onPointerEnter}
+      onPointerLeave={onPointerLeave}
+      onClick={onClick}
+      className={cn(
+        'w-full flex items-center gap-1.5 px-2 py-1.5 rounded-md',
+        'text-xs text-left',
+        'hover:bg-accent transition-colors',
+        'focus:outline-none focus:bg-accent',
+        isSelected && 'bg-accent'
+      )}
+      data-testid={`project-theme-${option.value}`}
+    >
+      <Icon className="w-3.5 h-3.5" style={{ color: option.color }} />
+      <span>{option.label}</span>
+    </button>
+  );
+});
+
+// Reusable theme column component
+interface ThemeColumnProps {
+  title: string;
+  icon: LucideIcon;
+  themes: ThemeOption[];
+  selectedTheme: string | null;
+  onPreviewEnter: (value: string) => void;
+  onPreviewLeave: (e: React.PointerEvent) => void;
+  onSelect: (value: string) => void;
+}
+
+const ThemeColumn = memo(function ThemeColumn({
+  title,
+  icon: Icon,
+  themes,
+  selectedTheme,
+  onPreviewEnter,
+  onPreviewLeave,
+  onSelect,
+}: ThemeColumnProps) {
+  return (
+    <div className="flex-1">
+      <div className="flex items-center gap-1.5 px-2 py-1.5 text-xs font-medium text-muted-foreground">
+        <Icon className="w-3 h-3" />
+        {title}
+      </div>
+      <div className="space-y-0.5">
+        {themes.map((option) => (
+          <ThemeButton
+            key={option.value}
+            option={option}
+            isSelected={selectedTheme === option.value}
+            onPointerEnter={() => onPreviewEnter(option.value)}
+            onPointerLeave={onPreviewLeave}
+            onClick={() => onSelect(option.value)}
+          />
+        ))}
+      </div>
+    </div>
+  );
+});
 
 interface ProjectContextMenuProps {
   project: Project;
@@ -19,18 +115,30 @@ export function ProjectContextMenu({
   onEdit,
 }: ProjectContextMenuProps) {
   const menuRef = useRef<HTMLDivElement>(null);
-  const { moveProjectToTrash } = useAppStore();
+  const {
+    moveProjectToTrash,
+    theme: globalTheme,
+    setTheme,
+    setProjectTheme,
+    setPreviewTheme,
+  } = useAppStore();
   const [showRemoveDialog, setShowRemoveDialog] = useState(false);
+  const [showThemeSubmenu, setShowThemeSubmenu] = useState(false);
+  const themeSubmenuRef = useRef<HTMLDivElement>(null);
+
+  const { handlePreviewEnter, handlePreviewLeave } = useThemePreview({ setPreviewTheme });
 
   useEffect(() => {
     const handleClickOutside = (event: MouseEvent) => {
       if (menuRef.current && !menuRef.current.contains(event.target as Node)) {
+        setPreviewTheme(null);
         onClose();
       }
     };
 
     const handleEscape = (event: KeyboardEvent) => {
       if (event.key === 'Escape') {
+        setPreviewTheme(null);
         onClose();
       }
     };
@@ -42,7 +150,7 @@ export function ProjectContextMenu({
       document.removeEventListener('mousedown', handleClickOutside);
       document.removeEventListener('keydown', handleEscape);
     };
-  }, [onClose]);
+  }, [onClose, setPreviewTheme]);
 
   const handleEdit = () => {
     onEdit(project);
@@ -52,6 +160,17 @@ export function ProjectContextMenu({
     setShowRemoveDialog(true);
   };
 
+  const handleThemeSelect = (value: string) => {
+    setPreviewTheme(null);
+    if (value !== '') {
+      setTheme(value as ThemeMode);
+    } else {
+      setTheme(globalTheme);
+    }
+    setProjectTheme(project.id, value === '' ? null : (value as ThemeMode));
+    setShowThemeSubmenu(false);
+  };
+
   const handleConfirmRemove = () => {
     moveProjectToTrash(project.id);
     onClose();
@@ -62,7 +181,7 @@ export function ProjectContextMenu({
       <div
         ref={menuRef}
         className={cn(
-          'fixed z-[100] min-w-48 rounded-lg',
+          'fixed min-w-48 rounded-lg',
           'bg-popover text-popover-foreground',
           'border border-border shadow-lg',
           'animate-in fade-in zoom-in-95 duration-100'
@@ -70,6 +189,7 @@ export function ProjectContextMenu({
         style={{
           top: position.y,
           left: position.x,
+          zIndex: Z_INDEX.CONTEXT_MENU,
         }}
         data-testid="project-context-menu"
       >
@@ -88,6 +208,96 @@ export function ProjectContextMenu({
             <span>Edit Name & Icon</span>
           </button>
 
+          {/* Theme Submenu Trigger */}
+          <div className="relative">
+            <button
+              onMouseEnter={() => setShowThemeSubmenu(true)}
+              onClick={() => setShowThemeSubmenu(!showThemeSubmenu)}
+              className={cn(
+                'w-full flex items-center gap-2 px-3 py-2 rounded-md',
+                'text-sm font-medium text-left',
+                'hover:bg-accent transition-colors',
+                'focus:outline-none focus:bg-accent'
+              )}
+              data-testid="theme-project-button"
+            >
+              <Palette className="w-4 h-4" />
+              <span className="flex-1">Project Theme</span>
+              {project.theme && (
+                <span className="text-[10px] text-muted-foreground capitalize">
+                  {project.theme}
+                </span>
+              )}
+              <ChevronRight className="w-4 h-4 text-muted-foreground" />
+            </button>
+
+            {/* Theme Submenu */}
+            {showThemeSubmenu && (
+              <div
+                ref={themeSubmenuRef}
+                className={cn(
+                  'absolute left-full top-0 ml-1 min-w-[420px] rounded-lg',
+                  'bg-popover text-popover-foreground',
+                  'border border-border shadow-lg',
+                  'animate-in fade-in zoom-in-95 duration-100'
+                )}
+                style={{ zIndex: Z_INDEX.THEME_SUBMENU }}
+                onMouseLeave={() => {
+                  setShowThemeSubmenu(false);
+                  setPreviewTheme(null);
+                }}
+                data-testid="project-theme-submenu"
+              >
+                <div className="p-2">
+                  {/* Use Global Option */}
+                  <button
+                    onPointerEnter={() => handlePreviewEnter(globalTheme)}
+                    onPointerLeave={() => setPreviewTheme(null)}
+                    onClick={() => handleThemeSelect('')}
+                    className={cn(
+                      'w-full flex items-center gap-2 px-3 py-2 rounded-md',
+                      'text-sm font-medium text-left',
+                      'hover:bg-accent transition-colors',
+                      'focus:outline-none focus:bg-accent',
+                      !project.theme && 'bg-accent'
+                    )}
+                    data-testid="project-theme-global"
+                  >
+                    <Monitor className="w-4 h-4" />
+                    <span>Use Global</span>
+                    <span className="text-[10px] text-muted-foreground ml-1 capitalize">
+                      ({globalTheme})
+                    </span>
+                  </button>
+
+                  <div className="h-px bg-border my-2" />
+
+                  {/* Two Column Layout - Using reusable ThemeColumn component */}
+                  <div className="flex gap-2">
+                    <ThemeColumn
+                      title="Dark"
+                      icon={Moon}
+                      themes={PROJECT_DARK_THEMES}
+                      selectedTheme={project.theme ?? null}
+                      onPreviewEnter={handlePreviewEnter}
+                      onPreviewLeave={handlePreviewLeave}
+                      onSelect={handleThemeSelect}
+                    />
+                    <ThemeColumn
+                      title="Light"
+                      icon={Sun}
+                      themes={PROJECT_LIGHT_THEMES}
+                      selectedTheme={project.theme ?? null}
+                      onPreviewEnter={handlePreviewEnter}
+                      onPreviewLeave={handlePreviewLeave}
+                      onSelect={handleThemeSelect}
+                    />
+                  </div>
+                </div>
+              </div>
+            )}
+          </div>
+
           <button
             onClick={handleRemove}
             className={cn(