fix: add missing pg_conn fixture to conftest.py

Session-scoped psycopg2 fixture that skips gracefully when
POSTGRES_HOST is absent (local dev) and connects in CI. Required
by seeded_data/seeded_tracks fixtures in evolution API tests.

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

tests/conftest.py

@@ -11,6 +11,7 @@ tests.
 
 import os
 import pytest
+import psycopg2
 from peewee import SqliteDatabase
 
 # Set DATABASE_TYPE=postgresql so that the module-level SKIP_TABLE_CREATION
@@ -169,3 +170,39 @@ def track():
         t3_threshold=448,
         t4_threshold=896,
     )
+
+
+# ---------------------------------------------------------------------------
+# PostgreSQL integration fixture (used by test_evolution_*_api.py)
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture(scope="session")
+def pg_conn():
+    """Open a psycopg2 connection to the PostgreSQL instance for integration tests.
+
+    Reads connection parameters from the standard POSTGRES_* env vars that the
+    CI workflow injects when a postgres service container is running.  Skips the
+    entire session (via pytest.skip) when POSTGRES_HOST is not set, keeping
+    local runs clean.
+
+    The connection is shared for the whole session (scope="session") because
+    the integration test modules use module-scoped fixtures that rely on it;
+    creating a new connection per test would break those module-scoped fixtures.
+
+    Teardown: the connection is closed once all tests have finished.
+    """
+    host = os.environ.get("POSTGRES_HOST")
+    if not host:
+        pytest.skip("POSTGRES_HOST not set — PostgreSQL integration tests skipped")
+
+    conn = psycopg2.connect(
+        host=host,
+        port=int(os.environ.get("POSTGRES_PORT", "5432")),
+        dbname=os.environ.get("POSTGRES_DB", "paper_dynasty"),
+        user=os.environ.get("POSTGRES_USER", "postgres"),
+        password=os.environ.get("POSTGRES_PASSWORD", ""),
+    )
+    conn.autocommit = False
+    yield conn
+    conn.close()