Add Postgres table adapter with TableRepositoryInterface.

Introduce PostgresAdapter for dict-based row CRUD via psycopg3, including config, lazy exports, unit/integration tests with testcontainers, and an example UserTableRepository.

Co-authored-by: Cursor <[email protected]>

python_repositories/config/postgres_config.py

@@ -0,0 +1,42 @@
+"""PostgreSQL connection configuration."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+import os
+
+from python_utils import check_env
+
+from python_repositories.config.dotenv_loader import load_dotenv
+
+
+@dataclass(frozen=True)
+class PostgresConfig:
+    """Configuration for connecting to PostgreSQL."""
+
+    uri: str
+    table: str
+    primary_key: str = "id"
+
+    @classmethod
+    def from_env(
+        cls,
+        uri_env_var_name: str = "POSTGRES_URI",
+        table_env_var_name: str = "POSTGRES_TABLE",
+        primary_key_env_var_name: str = "POSTGRES_PRIMARY_KEY",
+        *,
+        use_dotenv: bool = True,
+    ) -> PostgresConfig:
+        """Load configuration from environment variables."""
+        if use_dotenv:
+            load_dotenv()
+        env_var_names = {uri_env_var_name, table_env_var_name}
+        check_env(env_var_names)
+        primary_key = os.getenv(primary_key_env_var_name)
+        if primary_key is None or primary_key == "":
+            primary_key = "id"
+        return cls(
+            uri=str(os.getenv(uri_env_var_name)),
+            table=str(os.getenv(table_env_var_name)),
+            primary_key=primary_key,
+        )