feat(geoportal): nginx tile cache + PMTiles overview layers + tippecanoe pipeline

- Add nginx reverse proxy cache in front of Martin (2GB, 1h TTL, stale serving, CORS)
- Martin no longer exposes host port — all traffic routed through tile-cache on :3010
- Add PMTiles support in map-viewer.tsx (conditional: NEXT_PUBLIC_PMTILES_URL env var)
  - When set: single PMTiles source for UAT + administrativ layers (z0-z14, ~5ms/tile)
  - When empty: fallback to Martin tile sources (existing behavior, zero breaking change)
- Add tippecanoe Docker service (profiles: tools) for on-demand PMTiles generation
- Add rebuild-overview-tiles.sh: ogr2ogr export → tippecanoe → MinIO atomic upload
- Install pmtiles npm package for MapLibre protocol registration

Performance impact:
- nginx cache: 10-100x faster on repeat tile requests, zero PostGIS load on cache hit
- PMTiles: sub-10ms overview tiles, zero PostGIS load for z0-z14

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

package.json

@@ -26,6 +26,7 @@
     "next-auth": "^4.24.13",
     "next-themes": "^0.4.6",
     "nodemailer": "^7.0.13",
+    "pmtiles": "^4.4.0",
     "proj4": "^2.20.3",
     "qrcode": "^1.5.4",
     "radix-ui": "^1.4.3",