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>

martin.yaml

@@ -84,7 +84,7 @@ postgres:
       geometry_column: geom
       srid: 3844
       bounds: [20.2, 43.5, 30.0, 48.3]
-      minzoom: 14
+      minzoom: 17
       maxzoom: 18
       properties:
         object_id: text
@@ -139,7 +139,7 @@ postgres:
       geometry_column: geom
       srid: 3844
       bounds: [20.2, 43.5, 30.0, 48.3]
-      minzoom: 15
+      minzoom: 17
       maxzoom: 18
       properties:
         object_id: text