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

.opencode/skills/theme-system/references/adding-themes.md

@@ -0,0 +1,51 @@
+---
+title: Adding Themes
+---
+
+# Adding Themes
+
+## Custom Themes (User)
+
+Drop a JSON file into `~/.config/openchamber/themes/`. No rebuild needed.
+
+1. Create theme file (e.g., `my-theme.json`)
+2. In app: **Settings → Theme → Reload themes**
+3. Select from dropdown
+
+See `docs/CUSTOM_THEMES.md` for full format reference.
+
+## Built-in Themes (Development)
+
+### 1. Create JSON Files
+
+Add to `packages/ui/src/lib/theme/themes/`:
+- `<id>-light.json`
+- `<id>-dark.json`
+
+Use existing themes (e.g., `flexoki-dark.json`) as reference for the full structure.
+
+### 2. Register in presets.ts
+
+```typescript
+import mytheme_light_Raw from './mytheme-light.json';
+import mytheme_dark_Raw from './mytheme-dark.json';
+
+export const presetThemes: Theme[] = [
+  // ... existing themes
+  mytheme_light_Raw as Theme,
+  mytheme_dark_Raw as Theme,
+];
+```
+
+### 3. Validate
+
+```bash
+bun run type-check && bun run lint && bun run build
+```
+
+## Key Files
+
+- Theme types: `packages/ui/src/types/theme.ts`
+- Presets: `packages/ui/src/lib/theme/themes/presets.ts`
+- Example: `packages/ui/src/lib/theme/themes/flexoki-dark.json`
+- Custom themes doc: `docs/CUSTOM_THEMES.md`