feat: POTUS Fleet tracker, Docker secrets, route fix, SQLite->JSON migration

- Add Docker Swarm secrets _FILE support (AIS_API_KEY_FILE, etc.)
- Fix flight route lookup: pass lat/lng to adsb.lol routeset API, return airport names
- Replace SQLite plane_alert DB with JSON file + O(1) category color mapping
- Add POTUS Fleet (AF1, AF2, Marine One) with hardcoded ICAO overrides
- Add tracked_names enrichment from Excel data with POTUS protection
- Add oversized gold-ringed POTUS SVG icons on map
- Add POTUS Fleet tracker panel in WorldviewLeftPanel with fly-to
- Overhaul tracked flight labels: zoom-gated, PIA hidden, color-mapped
- Add orange color to trackedIconMap, soften white icon strokes
- Fix NewsFeed Wikipedia links to use alert_wiki slug


Former-commit-id: 6f952104c1

frontend/src/lib/api.ts

@@ -1,6 +1,7 @@
 // All API calls use relative paths (e.g. /api/flights).
-// Next.js rewrites them at the server level to BACKEND_URL (set in docker-compose
-// or .env.local for dev). This means:
+// The catch-all route handler at src/app/api/[...path]/route.ts proxies them
+// to BACKEND_URL at runtime (set in docker-compose or .env.local for dev).
+// This means:
 //   - No build-time baking of the backend URL into the client bundle
 //   - BACKEND_URL=http://backend:8000 works via Docker internal networking
 //   - Only port 3000 needs to be exposed externally