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/DependencyBadge.tsx

@@ -1,5 +1,6 @@
 import { AlertTriangle, GitBranch, Check } from 'lucide-react'
 import type { Feature } from '../lib/types'
+import { Badge } from '@/components/ui/badge'
 
 interface DependencyBadgeProps {
   feature: Feature
@@ -38,14 +39,13 @@ export function DependencyBadge({ feature, allFeatures = [], compact = false }:
   if (compact) {
     // Compact view for card displays
     return (
-      <div
-        className={`
-          inline-flex items-center gap-1 text-xs px-2 py-0.5 rounded-full font-mono
-          ${isBlocked
-            ? 'bg-neo-danger/20 text-neo-danger'
-            : 'bg-neo-neutral-200 text-neo-text-secondary'
-          }
-        `}
+      <Badge
+        variant="outline"
+        className={`gap-1 font-mono text-xs ${
+          isBlocked
+            ? 'bg-destructive/10 text-destructive border-destructive/30'
+            : 'bg-muted text-muted-foreground'
+        }`}
         title={isBlocked
           ? `Blocked by ${blockingCount} ${blockingCount === 1 ? 'dependency' : 'dependencies'}`
           : `${satisfiedCount}/${dependencies.length} dependencies satisfied`
@@ -62,7 +62,7 @@ export function DependencyBadge({ feature, allFeatures = [], compact = false }:
             <span>{satisfiedCount}/{dependencies.length}</span>
           </>
         )}
-      </div>
+      </Badge>
     )
   }
 
@@ -70,15 +70,15 @@ export function DependencyBadge({ feature, allFeatures = [], compact = false }:
   return (
     <div className="flex items-center gap-2">
       {isBlocked ? (
-        <div className="flex items-center gap-1.5 text-sm text-neo-danger">
+        <div className="flex items-center gap-1.5 text-sm text-destructive">
           <AlertTriangle size={14} />
           <span className="font-medium">
             Blocked by {blockingCount} {blockingCount === 1 ? 'dependency' : 'dependencies'}
           </span>
         </div>
       ) : (
-        <div className="flex items-center gap-1.5 text-sm text-neo-text-secondary">
-          <Check size={14} className="text-neo-done" />
+        <div className="flex items-center gap-1.5 text-sm text-muted-foreground">
+          <Check size={14} className="text-primary" />
           <span>
             All {dependencies.length} {dependencies.length === 1 ? 'dependency' : 'dependencies'} satisfied
           </span>
@@ -102,7 +102,7 @@ export function DependencyIndicator({ feature }: { feature: Feature }) {
   if (isBlocked) {
     return (
       <span
-        className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-neo-danger/20 text-neo-danger"
+        className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-destructive/10 text-destructive"
         title={`Blocked by ${feature.blocking_dependencies?.length || 0} dependencies`}
       >
         <AlertTriangle size={12} />
@@ -112,7 +112,7 @@ export function DependencyIndicator({ feature }: { feature: Feature }) {
 
   return (
     <span
-      className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-neo-neutral-200 text-neo-text-secondary"
+      className="inline-flex items-center justify-center w-5 h-5 rounded-full bg-muted text-muted-foreground"
       title={`${dependencies.length} dependencies (all satisfied)`}
     >
       <GitBranch size={12} />