Add theme switching with three modes (system/light/dark) using Tailwind v4
class-based dark mode. Theme preference is persisted in localStorage and
defaults to the system's prefers-color-scheme. All components updated with
dark: variants for consistent dark mode rendering including SVG elements.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- Create /chat route with scrollable message list
- MessageBubble component with distinct user/assistant styles
- MessageList with auto-scroll-to-bottom on new messages
- Empty state display when no messages
- ChatMessage type definition in src/lib/types.ts
- Add browser globals to ESLint config for Svelte files
Closes#5
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
