Add self-hosted usage analytics: pageview tracking + admin stats dashboard

Records pageviews (path, referrer, browser/OS/device, IP, GeoIP country) via
a POST /api/track beacon into a new PageView table, and exposes aggregated
daily/breakdown stats behind a token-gated GET /api/admin/stats endpoint with
brute-force lockout. Frontend gets a /admin dashboard (charts + breakdown
tables) built on recharts, with a switchable per-day pageviews chart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

requirements.txt

@@ -8,6 +8,8 @@ SQLAlchemy[asyncio]>=2.0
 aiosqlite>=0.20      # dev / default DATABASE_URL
 asyncpg>=0.29        # production (PostgreSQL)
 pyotp>=2.9           # TOTP login
+user-agents>=2.2     # parse User-Agent for /track (self-hosted analytics)
+geoip2>=4.8           # resolve IP -> country from a local .mmdb file (no external calls)
 
 # NOTE: the legacy Flask/Jinja HTTP UI (api/routes.py, api/forms.py,
 # api/templates/) is dormant and its dependencies (Flask, Flask-WTF, etc.)