Strip border-radius, box-shadow, background, and backdrop-filter from
the sidebar toggle in both v2 and v3 frontends so the logo appears flat.

https://claude.ai/code/session_019Z4VJxzY7tcAuNkPAkvry9

The sidebar default-closed JS logic used 1024px but CSS media queries
used 768px, causing inconsistent behavior on tablets. Updated all
sidebar-related breakpoints to 1024px/1025px to match.

https://claude.ai/code/session_019Z4VJxzY7tcAuNkPAkvry9

Change IntersectionObserver threshold from 0.5 to 1.0 so items are only
marked as read when fully scrolled into view, reducing accidental
mark-as-read during fast scrolling.

Also fix unused Category import in perf test and add thicket config.json
to repository so future agents can use thicket CLI commands.

Closes NK-s2g59a

https://claude.ai/code/session_019Z4VJxzY7tcAuNkPAkvry9

- Fix V3 keyboard navigation delay (resolved NK-wjats7)
- Update V3 document title to 'neko' (resolved NK-4p3s91)
- Fix V3 neko logo/button position to be top-left fixed (resolved NK-89za3s)
- Improve FeedItems (React) stability with ref-based index tracking and robust tests
- Sync V3 styling and selection feedback with V2 patterns
- Rebuild production assets

- Remove duplicate neko logo from v3 sidebar
- Keep sidebar toggle button fixed at top-left even when sidebar is open
- Add top padding to v3 sidebar to prevent overlap with the fixed toggle button
- Update v3 tests to match UI changes

- Sync v3 dark/light theme colors with v2 defaults
- Fix v3 settings input/select contrast in dark mode
- Add logo emoji to v3 sidebar
- Fix duplicate key warnings and side-effect issues in FeedItems.tsx (v2)
- Rebuild production assets

- Update Makefile to correctly build and copy frontend-vanilla (v3) assets
- Fix frontend-vanilla/vite.config.ts to build to its own dist directory
- Normalize CSRF check path and exclude /api/logout to fix v3 session clearing
- Include latest built assets for v3