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>

.gitignore

@@ -6,3 +6,4 @@ __pycache__/
 frontend/node_modules/
 frontend/dist/
 frontend/.vite/
+geoip/*.mmdb