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/CommandAutocomplete.tsx

@@ -232,7 +232,7 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
   return (
     <div
       ref={containerRef}
-      className="absolute z-[100] min-w-0 w-full max-w-[450px] max-h-64 bg-background border border-border rounded-xl shadow-none bottom-full mb-2 left-0 flex flex-col"
+      className="absolute z-[100] min-w-0 w-full max-w-[450px] max-h-64 bg-background border-2 border-border/60 rounded-xl shadow-md bottom-full mb-2 left-0 flex flex-col"
     >
       <ScrollableOverlay outerClassName="flex-1 min-h-0" className="px-0 pb-2" fillContainer={false}>
         {loading ? (
@@ -251,7 +251,7 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
                   ref={(el) => { itemRefs.current[index] = el; }}
                   className={cn(
                     "flex items-start gap-2 px-3 py-2 cursor-pointer rounded-lg",
-                    index === selectedIndex && "bg-muted"
+                    index === selectedIndex && "bg-interactive-selection"
                   )}
                   onClick={() => onCommandSelect(command)}
                   onMouseEnter={() => setSelectedIndex(index)}