style(ui): rework light/dark theme to make it visually consistent

Rework the color system around warm neutrals and route hardcoded
surfaces through theme tokens for consistency.

- Theme tokens (index.css, ThemeContext): warm cream light mode and
  neutral charcoal dark mode, replacing the pure-white/blue-tinted
  palette; update PWA theme-color meta
- Code blocks: soft grey background in light mode via
  oneLight/oneDark, and drop the Tailwind Typography <pre> shell that
  framed the highlighter in a dark box
- Dropdowns/panels: convert CommandMenu, Quick Settings, and the JSON
  response block from hardcoded gray/slate to popover/muted/border
  tokens
- Git panel: Publish button purple -> primary blue
- Composer: drop top padding so the input sits flush with the thread

src/components/quick-settings-panel/constants.ts

@@ -16,7 +16,7 @@ export const HANDLE_POSITION_MAX = 90;
 export const DRAG_THRESHOLD_PX = 5;
 
 export const SETTING_ROW_CLASS =
-  'flex items-center justify-between p-3 rounded-lg bg-gray-50 dark:bg-gray-800 hover:bg-gray-100 dark:hover:bg-gray-700 transition-colors border border-transparent hover:border-gray-300 dark:hover:border-gray-600';
+  'flex items-center justify-between p-3 rounded-lg bg-muted/60 hover:bg-accent transition-colors border border-transparent hover:border-border';
 
 export const TOGGLE_ROW_CLASS = `${SETTING_ROW_CLASS} cursor-pointer`;