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/providers/ThemeProvider.tsx

@@ -6,30 +6,12 @@ interface ThemeProviderProps {
 }
 
 export const ThemeProvider: React.FC<ThemeProviderProps> = ({ children }) => {
-  const { theme, applyTheme, fontSize, applyTypography, padding, applyPadding } = useUIStore();
+  const { fontSize, applyTypography, padding, applyPadding } = useUIStore();
 
   React.useLayoutEffect(() => {
-    applyTheme();
     applyTypography();
     applyPadding();
-  }, [theme, applyTheme, fontSize, applyTypography, padding, applyPadding]);
-
-  React.useEffect(() => {
-
-    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
-
-    const handleChange = () => {
-      if (theme === 'system') {
-        applyTheme();
-      }
-    };
-
-    mediaQuery.addEventListener('change', handleChange);
-
-    return () => {
-      mediaQuery.removeEventListener('change', handleChange);
-    };
-  }, [theme, applyTheme]);
+  }, [fontSize, applyTypography, padding, applyPadding]);
 
   return <>{children}</>;
-};
+};