fix: update main.py imports for service subpackages

services/correlation.py was moved to services/shared/correlation.py,
services/event_bus.py to services/instance/event_bus.py, and
services/health_monitor.py to services/instance/health_monitor.py
but main.py was still importing from the old flat paths.

Updated main.py to import from the new subpackage paths via
__init__.py re-exports.

Quality gates: py_compile passed, ruff passed.

apps/api/src/main.py

@@ -41,9 +41,8 @@ from src.logging_config import (
     configure_logging,
 )
 from src.seeds.builtin_tool_types import seed_builtin_tool_types
-from src.services.correlation import CorrelationIdMiddleware
-from src.services.event_bus import InstanceEventBus
-from src.services.health_monitor import HealthMonitor
+from src.services.instance import InstanceEventBus, HealthMonitor
+from src.services.shared import CorrelationIdMiddleware
 
 # Configure logging early
 log_level = os.getenv("LOG_LEVEL", "INFO").upper()