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/TimelineDialog.tsx

@@ -117,7 +117,7 @@ export const TimelineDialog: React.FC<TimelineDialogProps> = ({ open, onOpenChan
                             return (
                                 <div
                                     key={message.info.id}
-                                    className="group flex items-center gap-2 py-1.5 hover:bg-muted/30 rounded transition-colors cursor-pointer"
+                                    className="group flex items-center gap-2 py-1.5 hover:bg-interactive-hover/30 rounded transition-colors cursor-pointer"
                                     onClick={() => {
                                         onScrollToMessage?.(message.info.id);
                                         onOpenChange(false);