feat(frontend): account dropdown with Google name in header nav

feat(auth+db): session-aware nav, ownership fix, admin hardening, schema cleanup

feat: rebrand to PaperMate, ARR review rubric, feedback form, UI improvements

Replace secret key masked div with password input + icon buttons

Logo to DM Serif Display, secret key masked with show/hide + copy actions

Switch step numbers to Playfair Display with thinner outline

Redesign step numbers as large outlined corner labels

Fix footer always sticks to bottom using flexbox layout

Reduce How it works to 3 steps, fix footer position on review page

Switch all icons to Remix Icon CDN (ri-* classes)

Redesign UI with dark/light mode, gold accent system, Be Vietnam Pro font

Initial implementation of AI research paper review system