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/session/DirectoryAutocomplete.tsx

@@ -292,7 +292,7 @@ export const DirectoryAutocomplete = React.forwardRef<DirectoryAutocompleteHandl
                 ref={(el) => { itemRefs.current[index] = el; }}
                 className={cn(
                   "flex items-center gap-2 px-3 py-1.5 cursor-pointer typography-ui-label",
-                  isSelected && "bg-muted"
+                  isSelected && "bg-interactive-selection"
                 )}
                 onClick={() => { handleSelectSuggestion(entry); onClose(); }}
                 onMouseEnter={() => setSelectedIndex(index)}