refactor(ui): migrate to shadcn/ui components and fix scroll issues

Migrate UI component library from custom implementations to shadcn/ui:
- Add shadcn/ui primitives (Button, Card, Dialog, Input, etc.)
- Replace custom styles with Tailwind CSS v4 theme configuration
- Remove custom-theme.css in favor of globals.css with @theme directive

Fix scroll overflow issues in multiple components:
- ProjectSelector: "New Project" button no longer overlays project list
- FolderBrowser: folder list now scrolls properly within modal
- AgentCard: log modal content stays within bounds
- ConversationHistory: conversation list scrolls correctly
- KanbanColumn: feature cards scroll within fixed height
- ScheduleModal: schedule form content scrolls properly

Key technical changes:
- Replace ScrollArea component with native overflow-y-auto divs
- Add min-h-0 to flex containers to allow proper shrinking
- Restructure dropdown layouts with flex-col for fixed footers

New files:
- ui/components.json (shadcn/ui configuration)
- ui/src/components/ui/* (20 UI primitive components)
- ui/src/lib/utils.ts (cn utility for class merging)
- ui/tsconfig.app.json (app-specific TypeScript config)

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

ui/src/components/KeyboardShortcutsHelp.tsx

@@ -1,5 +1,12 @@
 import { useEffect, useCallback } from 'react'
-import { X, Keyboard } from 'lucide-react'
+import { Keyboard } from 'lucide-react'
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+} from '@/components/ui/dialog'
+import { Badge } from '@/components/ui/badge'
 
 interface Shortcut {
   key: string
@@ -20,10 +27,11 @@ const shortcuts: Shortcut[] = [
 ]
 
 interface KeyboardShortcutsHelpProps {
+  isOpen: boolean
   onClose: () => void
 }
 
-export function KeyboardShortcutsHelp({ onClose }: KeyboardShortcutsHelpProps) {
+export function KeyboardShortcutsHelp({ isOpen, onClose }: KeyboardShortcutsHelpProps) {
   const handleKeyDown = useCallback(
     (e: KeyboardEvent) => {
       if (e.key === 'Escape' || e.key === '?') {
@@ -35,59 +43,49 @@ export function KeyboardShortcutsHelp({ onClose }: KeyboardShortcutsHelpProps) {
   )
 
   useEffect(() => {
-    window.addEventListener('keydown', handleKeyDown)
-    return () => window.removeEventListener('keydown', handleKeyDown)
-  }, [handleKeyDown])
+    if (isOpen) {
+      window.addEventListener('keydown', handleKeyDown)
+      return () => window.removeEventListener('keydown', handleKeyDown)
+    }
+  }, [isOpen, handleKeyDown])
 
   return (
-    <div
-      className="fixed inset-0 z-50 flex items-center justify-center bg-black/50"
-      onClick={onClose}
-    >
-      <div
-        className="neo-card p-6 max-w-md w-full mx-4"
-        onClick={(e) => e.stopPropagation()}
-      >
-        {/* Header */}
-        <div className="flex items-center justify-between mb-6">
-          <div className="flex items-center gap-2">
-            <Keyboard size={20} className="text-neo-accent" />
-            <h2 className="font-display text-lg font-bold">Keyboard Shortcuts</h2>
-          </div>
-          <button
-            onClick={onClose}
-            className="neo-btn p-1.5"
-            aria-label="Close"
-          >
-            <X size={16} />
-          </button>
-        </div>
+    <Dialog open={isOpen} onOpenChange={(open) => !open && onClose()}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="flex items-center gap-2">
+            <Keyboard size={20} className="text-primary" />
+            Keyboard Shortcuts
+          </DialogTitle>
+        </DialogHeader>
 
         {/* Shortcuts list */}
-        <ul className="space-y-2">
+        <ul className="space-y-1">
           {shortcuts.map((shortcut) => (
             <li
               key={shortcut.key}
-              className="flex items-center justify-between py-2 border-b border-neo-border/30 last:border-0"
+              className="flex items-center justify-between py-2 border-b border-border/50 last:border-0"
             >
-              <div className="flex items-center gap-2">
-                <kbd className="px-2 py-1 text-sm font-mono bg-neo-bg rounded border border-neo-border shadow-neo-sm min-w-[2rem] text-center">
+              <div className="flex items-center gap-3">
+                <kbd className="px-2 py-1 text-xs font-mono bg-muted rounded border border-border min-w-[2rem] text-center">
                   {shortcut.key}
                 </kbd>
-                <span className="text-neo-text">{shortcut.description}</span>
+                <span className="text-sm">{shortcut.description}</span>
               </div>
               {shortcut.context && (
-                <span className="text-xs text-neo-muted">{shortcut.context}</span>
+                <Badge variant="secondary" className="text-xs">
+                  {shortcut.context}
+                </Badge>
               )}
             </li>
           ))}
         </ul>
 
         {/* Footer */}
-        <p className="text-xs text-neo-muted text-center mt-6">
+        <p className="text-xs text-muted-foreground text-center pt-2">
           Press ? or Esc to close
         </p>
-      </div>
-    </div>
+      </DialogContent>
+    </Dialog>
   )
 }