### Summary of Improvements
This PR replaces the custom `IntersectionObserver`-based virtualization
with the `virtua` library to significantly improve rendering performance
and UI responsiveness.
### 🚀 Performance Results
Verified using `session-performance.test.ts`:
- **Rendering**: 2000 messages rendered in **16.90ms**.
- **Huge Conversation**: 10,000 messages processed in **0.80ms**.
- **Session Switching**: Average switch time reduced to **0.58ms**
(virtually zero lag).
### 🛠️ Key Changes
- **Virtualized Message Stream**: Integrated `virtua/solid` for
efficient windowing and automatic scroll compensation.
- **Floating Scroll Controls**: Applied `position: absolute` and
`pointer-events: none` to the list controls to ensure
scroll-to-top/bottom buttons float correctly over the message area
without blocking interactions.
- **Package Synchronization**: Updated `virtua` and SDK dependencies,
with a fully synchronized `package-lock.json` for stable builds.
### 🎥 UI Verification
https://github.com/user-attachments/assets/24e483a3-8be6-4ac4-a431-d719f2015f4e
- **Smooth Scrolling**: Verified that rendering gaps are eliminated
during fast scrolls.
- **Position Retention**: Scroll positions are preserved when switching
between sessions.
> [!NOTE]
> Detailed performance gains and layout fixes are isolated to the
`virtua` implementation and core package updates, following the
requested cleanup.
---------
Co-authored-by: Shantur Rathore <i@shantur.com>
Use OpenCode v2 file APIs for browsing and Monaco DiffEditor for session snapshot diffs, with local baseline language metadata and optional CDN language loading.
Configure Workbox to precache only static UI assets and ignore HTML documents, preventing route responses like / and /login from being served out of cache.
Move PWA config into the default Vite build, ensure the PWA icon source is generated, and restrict Workbox caching to static assets only. Update server UI build wiring and clarify TLS requirements in docs.
