feat: container monitoring backend core (PR-1)

- Add instance_events and health_checks tables with Alembic migration
- InstanceEventBus: typed pub/sub singleton with wildcard support
- HealthMonitor: async background loop polling containers every 15s
- SSE endpoint GET /events/stream with auth and connection limits
- Lifecycle hooks in tool_instances.py (create/start/stop/restart/delete)
- Structured JSON logging with correlation IDs
- 15 new unit tests (EventBus, HealthMonitor, MonitoringModels)

Quality gates: pytest 15 new passed, ruff clean

apps/api/tests/unit/test_monitoring_models.py

@@ -0,0 +1,143 @@
+"""Unit tests for monitoring models and migration compatibility."""
+
+import uuid
+from datetime import datetime
+
+import pytest
+from sqlalchemy import select
+
+from src.models.health_check import HealthCheck
+from src.models.instance_event import InstanceEvent
+from src.models.tool_instance import ToolInstance
+from src.models.user import User
+
+
+@pytest.mark.unit
+async def test_instance_event_creation(db_session) -> None:
+    """InstanceEvent model can be created and persisted."""
+    user = User(
+        id=uuid.uuid4(),
+        email="test@example.com",
+        name="Test",
+        authentik_id="auth-1",
+    )
+    db_session.add(user)
+    await db_session.commit()
+
+    instance = ToolInstance(
+        id=uuid.uuid4(),
+        name="test-instance",
+        display_name="Test Instance",
+        tool_type_id=uuid.uuid4(),
+        repository_id=uuid.uuid4(),
+        project_id=uuid.uuid4(),
+        owner_id=user.id,
+        status="pending",
+    )
+    db_session.add(instance)
+    await db_session.commit()
+
+    event = InstanceEvent(
+        instance_id=instance.id,
+        event_type="started",
+        status="starting",
+        message="Container starting...",
+        created_by=user.id,
+        event_metadata={"previous_status": "pending"},
+    )
+    db_session.add(event)
+    await db_session.commit()
+    await db_session.refresh(event)
+
+    assert event.id is not None
+    assert event.instance_id == instance.id
+    assert event.event_type == "started"
+    assert event.status == "starting"
+    assert event.created_by == user.id
+    assert event.event_metadata == {"previous_status": "pending"}
+    assert isinstance(event.created_at, datetime)
+
+
+@pytest.mark.unit
+async def test_health_check_creation(db_session) -> None:
+    """HealthCheck model can be created and persisted."""
+    user = User(
+        id=uuid.uuid4(),
+        email="test2@example.com",
+        name="Test2",
+        authentik_id="auth-2",
+    )
+    db_session.add(user)
+    await db_session.commit()
+
+    instance = ToolInstance(
+        id=uuid.uuid4(),
+        name="test-instance-2",
+        display_name="Test Instance 2",
+        tool_type_id=uuid.uuid4(),
+        repository_id=uuid.uuid4(),
+        project_id=uuid.uuid4(),
+        owner_id=user.id,
+        status="running",
+    )
+    db_session.add(instance)
+    await db_session.commit()
+
+    check = HealthCheck(
+        instance_id=instance.id,
+        container_status="running",
+        container_healthy=True,
+        tunnel_healthy=True,
+        exit_code=None,
+        probe_status="passed",
+        probe_output="OK",
+    )
+    db_session.add(check)
+    await db_session.commit()
+    await db_session.refresh(check)
+
+    assert check.id is not None
+    assert check.instance_id == instance.id
+    assert check.container_status == "running"
+    assert check.container_healthy is True
+    assert check.tunnel_healthy is True
+    assert isinstance(check.checked_at, datetime)
+
+
+@pytest.mark.unit
+async def test_instance_event_query_by_instance(db_session) -> None:
+    """InstanceEvent rows can be queried by instance_id."""
+    user = User(
+        id=uuid.uuid4(),
+        email="test3@example.com",
+        name="Test3",
+        authentik_id="auth-3",
+    )
+    db_session.add(user)
+    await db_session.commit()
+
+    instance = ToolInstance(
+        id=uuid.uuid4(),
+        name="test-instance-3",
+        display_name="Test Instance 3",
+        tool_type_id=uuid.uuid4(),
+        repository_id=uuid.uuid4(),
+        project_id=uuid.uuid4(),
+        owner_id=user.id,
+        status="pending",
+    )
+    db_session.add(instance)
+    await db_session.commit()
+
+    event = InstanceEvent(
+        instance_id=instance.id,
+        event_type="created",
+        status="pending",
+    )
+    db_session.add(event)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(InstanceEvent).where(InstanceEvent.instance_id == instance.id)
+    )
+    assert result.scalar_one() is not None