perf(geoportal): extend PMTiles to z18 — eliminate Martin for terenuri/cladiri entirely

PMTiles now covers z0-z18 (full zoom range). Martin sources kept only for
selection highlight and fallback when PMTiles not configured.
All terenuri/cladiri fill/line/label layers served from PMTiles when active.
Zero PostGIS load for tile rendering at any zoom level.

File will be ~1-2 GB but eliminates all cold-load latency.

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=16 \
-  --base-zoom=16 \
+  --maximum-zoom=18 \
+  --base-zoom=18 \
   --drop-densest-as-needed \
   --detect-shared-borders \
   --simplification=10 \