feat(map): self-hosted PMTiles map tiles, remove alert toast spam

- Replace OpenStreetMap CDN with self-hosted Protomaps PMTiles
  (Wisconsin + Florida regional extracts, served from nginx)
- Add protomaps-leaflet for vector tile rendering in dark theme
- Update CSP to remove openstreetmap.org, add blob: for vector workers
- Add nginx location block for /tiles/ with byte range support
- Mount tiles directory as volume (not baked into image)
- Remove alert_fired/alert_resolved toast notifications that spammed
  "undefined" at fleet scale — dashboard still updates via query invalidation
- Add *.pmtiles to .gitignore (large binaries)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -50,4 +50,7 @@ docs/comparison-*.md
 
 # Local dev tools (mock servers, screenshot automation)
 tools/dev/
+
+# PMTiles map data (large binaries, downloaded per-region)
+frontend/public/tiles/*.pmtiles
 fleet-dashboard.png