feat: add comprehensive screenshot snapshots for visual regression testing

- Add 45 PNG snapshots covering all pages and UI states
- Include device variations (desktop, mobile, tablet) for each state
- Enable visual diff comparison on GitHub for UI changes
- Remove snapshots from .gitignore to include in version control

Snapshot coverage:
- Root page: 3 snapshots
- Projects page: 6 snapshots (default, empty states)
- Project detail: 9 snapshots (default, filters-expanded, new-chat-modal)
- Session detail: 18 snapshots (default, sidebar-open across 3 session UUIDs)
- Error pages: 9 snapshots (404, invalid-project, invalid-session)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -12,7 +12,6 @@
 /playwright-report/
 /blob-report/
 /playwright/.cache/
-/e2e/snapshots/
 
 # next.js
 /.next/