Introduce ChatQuotaExhaustedBanner component that displays a pink gradient
banner with an "Unlock your membership to continue" CTA when a guest user's
free chat quota has been exhausted. The banner is shown in ChatScreen when
isGuest is true, quota has loaded, and the chat state machine's
quotaExceededTrigger has been incremented by a quota guard. Default click
navigates to /subscription, with an optional onUnlock callback for
overrides/tests. Styles align with the existing splash and sidebar VIP
card visual language.
- Fix chat components barrel to properly export all component modules
- Remove interceptor exports from API services barrel
- Regenerate store barrel files (auth, chat, sidebar, user) using barrelsby
- Move state management from `src/contexts` to `src/stores` (zustand-based)
- Update barrelsby config to include new stores directory
- Add bottom-sheet and auth-background components
- Auto-open browser on dev server ready in VS Code launch config
- Refresh generated barrel index files
- Remove unused CharacterIntro export from chat components index
- Drop stale JSDoc block from splash-screen server component
- Set mobile shell background to explicit black so the desktop area outside the 500px viewport is black instead of inheriting from parent