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/sections/commands/AgentSelector.tsx

@@ -120,7 +120,7 @@ export const AgentSelector: React.FC<AgentSelectorProps> = ({
                 <DropdownMenu>
                     <DropdownMenuTrigger asChild>
                         <div className={cn(
-                            'flex items-center gap-2 px-2 rounded-lg bg-accent/20 border border-border/20 cursor-pointer hover:bg-accent/30 h-6 w-fit',
+                            'flex items-center gap-2 px-2 rounded-lg bg-interactive-selection/20 border border-border/20 cursor-pointer hover:bg-interactive-hover/30 h-6 w-fit',
                             className
                         )}>
                             <RiRobot2Line className="h-3 w-3 flex-shrink-0 text-muted-foreground" />