feat: introduced a token-based theming system across the UI

* feat: added themes system

* feat: smart sidebar auto-hide for files/diff tabs + lower files sidebar threshold

* feat: added Checkbox component and update theming

- Add reusable Checkbox component for toggles across UI
- Replace several inputs with Checkbox in settings and commands panels
- Add DiffIcon and apply surface/border theming to key UI areas

* feat: Add convert-vscode-theme.cjs to convert VS Code themes to OpenChamber format

* refactor: remove unused permission logic from ChatInput

- Remove unused permission rules parsing logic from ChatInput
- Memoize renderTheme in DiffWorkerProvider to avoid unnecessary recalculations
- Remove forceOpaque helper in vscode theme adapter

* fix: guard VSCode theme loading in MarkdownRenderer

* feat: add custom user themes loading and reload

- Load user themes from ~/.config/openchamber/themes at runtime
- Expose /api/config/themes to fetch custom themes
- Allow theme reloading from Settings → Theme → Reload themes in the UI

packages/ui/src/components/chat/PermissionCard.tsx

@@ -313,7 +313,7 @@ export const PermissionCard: React.FC<PermissionCardProps> = ({
           <div className="px-2 py-1.5 border-b border-border/20 bg-muted/5">
             <div className="flex items-center justify-between">
               <div className="flex items-center gap-2">
-                <RiQuestionLine className="h-3.5 w-3.5 text-yellow-500" />
+                <RiQuestionLine className="h-3.5 w-3.5 text-[var(--status-warning)]" />
                 <span className="typography-meta font-medium text-muted-foreground">
                   Permission Required
                 </span>