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/src/models/__init__.py

@@ -1,6 +1,8 @@
 from src.models.base import Base
 from src.models.config_profile import ConfigProfile, ConfigProfileInclude
 from src.models.git_repository import GitRepository
+from src.models.health_check import HealthCheck
+from src.models.instance_event import InstanceEvent
 from src.models.project import Project
 from src.models.ssh_key import SSHKey
 from src.models.terminal_session import TerminalSessionModel
@@ -15,6 +17,8 @@ __all__ = [
     "ConfigProfile",
     "ConfigProfileInclude",
     "GitRepository",
+    "HealthCheck",
+    "InstanceEvent",
     "Project",
     "SSHKey",
     "TerminalSessionModel",