perf(geoportal): extend PMTiles to z16 — near-zero PostGIS load for tile serving

- PMTiles now covers z0-z16 (was z0-z14) for terenuri + cladiri
- Martin only serves z17-z18 (very close zoom, few features per tile)
- map-viewer: PMTiles layers serve z13-z16 for terenuri, z14-z16 for cladiri
- Labels at z16 now from PMTiles (cadastral_ref included in tiles)
- Remove failed compound index from postgis-setup.sql

This eliminates PostgreSQL as bottleneck for 99% of tile requests.
PMTiles file will be ~300-500MB (vs 104MB at z14).

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

prisma/postgis-setup.sql

@@ -59,10 +59,6 @@ WHERE geometry IS NOT NULL AND geom IS NULL;
 CREATE INDEX IF NOT EXISTS gis_feature_geom_idx
   ON "GisFeature" USING GIST (geom);
 
--- Compound index: layerId + spatial — Martin queries filter by layer via views
-CREATE INDEX IF NOT EXISTS gis_feature_layer_geom_idx
-  ON "GisFeature" ("layerId", geom) WHERE geom IS NOT NULL;
-
 -- B-tree index on layerId for view filtering (LIKE 'TERENURI%', 'CLADIRI%')
 CREATE INDEX IF NOT EXISTS gis_feature_layer_id_idx
   ON "GisFeature" ("layerId");