[codex] frontend dynamic redesign

[lsdragst-a11y]

Summary

• Adds the cinematic landing experience, refreshed NoteGen brand mark/favicon, and immersive login/register screens with interactive auth character behavior.
• Updates the public notebook catalog so guest users can browse public examples without auth blocking, personal progress panels, or misleading offline chrome.
• Improves mobile note workspace behavior with non-sticky mobile chat flow and an accessible chapter drawer focus loop.
• Replaces remaining raw image usage with Next Image in key visual components and documents the frontend redesign plan.

Impact

This makes the first-run and auth experience feel more dynamic and brand-led while keeping the app usable on mobile and with reduced visual noise. Public examples now work as an actual browseable entry point for unauthenticated users.

Validation

• npm test
• npx tsc --noEmit
• npm run lint
• npm run build
• Browser spot checks for /, /login, /register, /notebooks?filter=public, and mobile note drawer focus behavior.