change that GameplayDatabase can have different backends, sqlite and postgresql with a Template example backend

server/database/backend/__init__.py

@@ -0,0 +1,25 @@
+from .Template import GameplayBackendTemplate
+
+class GameplayBackendBuilder:
+  @staticmethod
+  def build(backend:str="sqlite", db_path:str|None=None, busy_timeout_ms:int=5000, pg_dsn:str|None=None, pg_min_size:int=1, pg_max_size:int=5) -> GameplayBackendTemplate:
+    normalized = (backend or "sqlite").strip().lower()
+
+    if normalized == "postgresql" or normalized == "postgres":
+      from .PostgresqlGameplayBackend import PostgresqlGameplayBackend
+      if not pg_dsn:
+        raise ValueError("pg_dsn is required for the postgresql backend")
+      return PostgresqlGameplayBackend(
+        dsn=pg_dsn,
+        min_size=pg_min_size,
+        max_size=pg_max_size,
+        sqlite_migration_path=db_path,
+      )
+
+    if normalized == "sqlite":
+      from .SqliteGameplayBackend import SqliteGameplayBackend
+      if not db_path:
+        raise ValueError("db_path is required for the sqlite backend")
+      return SqliteGameplayBackend(db_path=db_path, busy_timeout_ms=busy_timeout_ms)
+
+    raise ValueError(f"Unknown gameplay backend: {backend!r}. Choose 'sqlite' or 'postgresql'.")