refactor: remove test.db, use only posterg.db for all environments

- Simplified Database.php determineDatabasePath to always use posterg.db
- Removed test.db auto-detection based on php_sapi_name
- Removed test.db targets from justfile (migrate-test removed)
- Removed CreateTestDatabase.php fixture script
- Updated migrate.sh to only init posterg.db
- Updated setup-dev.sh to init posterg.db
- Updated run-tests.php (removed DB_ENV=test env var)
- Updated deploy-db to use posterg.db
- Removed test.db file

refactor: remove empty fixtures directory

scripts/setup-dev.sh

@@ -34,12 +34,12 @@ else
     echo "✓ Cloned php-live-reload"
 fi
 
-# Create test database if needed
-if [ ! -f "storage/test.db" ]; then
+# Create posterg.db if needed
+if [ ! -f "storage/posterg.db" ]; then
     echo ""
-    echo "📊 Creating test database..."
-    sqlite3 storage/test.db < storage/schema.sql
-    echo "✓ Created test database"
+    echo "📊 Creating posterg.db…"
+    sqlite3 storage/posterg.db < storage/schema.sql
+    echo "✓ Created posterg.db"
 fi
 
 # Create data directories