feat: ledger chain verification + security hardening + UI cleanup\n\nLedger:\n- Add verify_block/verify_chain/rehash_chain to LedgerHasher\n- Fix timestamp precision mismatch (microseconds vs MongoDB milliseconds)\n- Auto-repair legacy blocks on first view\n- New GET /api/ledger/<id>/verify endpoint with auth\n- Blockchain Audit Trail card in paper detail with validity badge\n\nSecurity:\n- Auto-generate SECRET_KEY if using insecure default\n- Security response headers (X-Content-Type-Options, X-Frame-Options, etc.)\n- Session cookie hardening (Secure flag, SameSite, HttpOnly)\n- Auth required on all search API endpoints\n- WebSocket auth: reject unauthenticated connections, validate room joins\n- Password policy (8+ chars, upper/lower/digit)\n- Session fixation prevention (clear session on login/register)\n- Rate limiting on login (10/15min) and register (5/15min)\n- XSS protection: safe_mode markdown + script/iframe stripping\n- Safer IP detection in SecurityManager\n\nUI/UX:\n- Strip redundant Final Scores table from overall assessment\n- Enable markdown tables extra for proper rendering\n- Add table CSS styling in paper detail\n- Remove console.log noise from browser templates\n- Reduce terminal logging from DEBUG to INFO\n- Fix duplicate raise in app.py\n- Fix ledger blueprint prefix (/api -> /api/ledger)

Refactor notification system and improve UI responsiveness

Enhance PDF report generation: improve text formatting, add title wrapping, and adjust layout styles

Release V3.0: Complete AI stack upgrade with multi-provider fallback

Version 2.0: Modern Academia Theme + Analytics Fixes + Live Analysis Log

Update README and .env.example

Major update: Batch review functionality, in-app notifications, academic UI redesign