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>

scripts/rebuild-overview-tiles.sh

@@ -83,8 +83,8 @@ tippecanoe \
   --named-layer=gis_terenuri:terenuri_overview.fgb \
   --named-layer=gis_cladiri:cladiri_overview.fgb \
   --minimum-zoom=0 \
-  --maximum-zoom=14 \
-  --base-zoom=14 \
+  --maximum-zoom=16 \
+  --base-zoom=16 \
   --drop-densest-as-needed \
   --detect-shared-borders \
   --simplification=10 \