fix: stop patching wiregui.db globally — broke e2e tests

Remove module-level engine/session replacement that affected all tests
including e2e. The test engine is now only used via the session fixture,
so e2e tests keep using the real DB the app writes to.

tests/conftest.py

@@ -1,11 +1,9 @@
 """Shared test fixtures — async DB session using a test database.
 
-The module-level code below replaces ``wiregui.db.engine`` and
-``wiregui.db.async_session`` with instances pointing at the **test** database
-*before* any test (or other module) can grab a reference to the originals.
-This means every ``from wiregui.db import async_session`` — whether in test
-files or in production code like ``wiregui.utils.server_key`` — will get the
-test-database session maker.
+Unit tests use the ``session`` fixture, which provides a per-test
+savepoint-isolated session on a dedicated test engine.  E2E tests do NOT
+use this fixture and are therefore unaffected — they keep using the real
+``wiregui.db.async_session`` that talks to the app's database.
 """
 
 import os
@@ -13,10 +11,9 @@ from collections.abc import AsyncGenerator
 
 import pytest_asyncio
 from sqlalchemy import text
-from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
 from sqlmodel import SQLModel
 
-import wiregui.db as _db_module
 from wiregui.config import get_settings
 
 # All models must be imported so SQLModel.metadata knows about them
@@ -60,21 +57,14 @@ def _ensure_test_db_sync():
 
 _ensure_test_db_sync()
 
-# ---------------------------------------------------------------------------
-# Replace the production engine/session in wiregui.db at import time so that
-# every module that does ``from wiregui.db import async_session`` picks up the
-# test database.  This MUST happen before test modules are collected (which
-# triggers their top-level imports).
-# ---------------------------------------------------------------------------
+# Test engine — only used by the ``session`` fixture and unit tests.
+# NOT assigned to wiregui.db so e2e tests are unaffected.
 _test_engine = create_async_engine(TEST_DATABASE_URL)
-_test_session_factory = async_sessionmaker(_test_engine, expire_on_commit=False)
-_db_module.engine = _test_engine
-_db_module.async_session = _test_session_factory
 
 
-@pytest_asyncio.fixture(scope="session", autouse=True)
-async def _setup_test_tables():
-    """Create all tables once at the start of the test session, drop at end."""
+@pytest_asyncio.fixture(scope="session")
+async def _test_tables():
+    """Create all tables once per test session, drop at end."""
     async with _test_engine.begin() as conn:
         await conn.run_sync(SQLModel.metadata.create_all)
     yield
@@ -84,7 +74,7 @@ async def _setup_test_tables():
 
 
 @pytest_asyncio.fixture
-async def session() -> AsyncGenerator[AsyncSession]:
+async def session(_test_tables) -> AsyncGenerator[AsyncSession]:
     """Per-test session with transaction isolation.
 
     The session is bound to a connection-level transaction that is always