perf(martin+postgres): connection pool limit + compound indexes + minzoom alignment

- Martin: pool_size=8 (prevents overwhelming PostgreSQL with concurrent queries)
- Martin: gis_terenuri minzoom 10→14, gis_cladiri minzoom 12→15
  (PMTiles serves z0-z14, no point in Martin generating those)
- PostGIS: add compound index layerId+geom for Martin view queries
- PostGIS: add B-tree index on layerId for LIKE filtering in views

Fixes 90% CPU on PostgreSQL during cold tile loads at detail zoom levels.

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

martin.yaml

@@ -4,6 +4,7 @@
 
 postgres:
   connection_string: ${DATABASE_URL}
+  pool_size: 8
   default_srid: 3844
   auto_publish: false
   tables:
@@ -83,7 +84,7 @@ postgres:
       geometry_column: geom
       srid: 3844
       bounds: [20.2, 43.5, 30.0, 48.3]
-      minzoom: 10
+      minzoom: 14
       maxzoom: 18
       properties:
         object_id: text
@@ -138,7 +139,7 @@ postgres:
       geometry_column: geom
       srid: 3844
       bounds: [20.2, 43.5, 30.0, 48.3]
-      minzoom: 12
+      minzoom: 15
       maxzoom: 18
       properties:
         object_id: text