feat: add chat page layout with message list and bubble components

- 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>

implementation-plans/issue-005.md

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+---
+---
+
+# Issue #5: Chat page layout and message list component
+
+**Status:** COMPLETED
+**Issue:** https://git.shahondin1624.de/llm-multiverse/llm-multiverse-ui/issues/5
+**Branch:** `feature/issue-5-chat-layout`
+
+## Summary
+
+Build the `/chat` route with scrollable message list, user/assistant message bubbles, auto-scroll, and empty state. Uses Svelte 5 runes.
+
+## Acceptance Criteria
+
+- [x] `/chat` route created
+- [x] Scrollable message list component
+- [x] Distinct user and assistant message bubble styles
+- [x] Auto-scroll to bottom on new messages
+- [x] Svelte 5 runes used for reactive message state (`$state`, `$derived`)
+- [x] Empty state shown when no messages
+
+## Deviations
+
+- Added `globals` package to ESLint config for browser globals in Svelte files (fixes `Element`/`HTMLDivElement` not defined errors).