feat: add PostGIS extension to dev PostgreSQL

- Add postgis to postgresql_16.withPackages alongside timescaledb
- Enable postgis extension on towerops_dev and towerops_test databases

nix/shell.nix

@@ -26,8 +26,11 @@
 }:
 
 let
-  # PostgreSQL with TimescaleDB extension
-  pg = postgresql_16.withPackages (ps: [ ps.timescaledb ]);
+  # PostgreSQL with TimescaleDB and PostGIS extensions
+  pg = postgresql_16.withPackages (ps: [
+    ps.timescaledb
+    ps.postgis
+  ]);
 
   # PostgreSQL data directory (local to project)
   pgDataDir = ".nix-postgres";
@@ -108,11 +111,14 @@ let
         ${pg}/bin/createdb -h ${pgHost} -p ${pgPort} -U $USER $db
     done
 
-    # Enable TimescaleDB extension for dev and test databases
+    # Enable TimescaleDB and PostGIS extensions for dev and test databases
     for db in towerops_dev towerops_test; do
       ${pg}/bin/psql -h ${pgHost} -p ${pgPort} -U $USER -d $db -c \
         "CREATE EXTENSION IF NOT EXISTS timescaledb CASCADE;" 2>/dev/null || \
         echo "⚠️  TimescaleDB not available for $db (optional)"
+      ${pg}/bin/psql -h ${pgHost} -p ${pgPort} -U $USER -d $db -c \
+        "CREATE EXTENSION IF NOT EXISTS postgis CASCADE;" 2>/dev/null || \
+        echo "⚠️  PostGIS not available for $db (optional)"
     done
 
     echo "✓ PostgreSQL started successfully"