fix: skip intermediate 'starting' notifications, only notify on failed/successful attempts

- lifecycle_hooks.publish_lifecycle_event now skips notification creation
  when event_type='instance.started' and status='starting'
- Users only see notifications for terminal states:
  - Failed: instance.error
  - Successful: instance.health_changed with status='running'
- Updated integration tests to verify new behavior:
  - test_lifecycle_started_intermediate_skips_notification
  - test_lifecycle_running_creates_notification

Quality gates: pytest 42 passed, ruff clean

apps/api/src/services/lifecycle_hooks.py

@@ -118,6 +118,14 @@ async def publish_lifecycle_event(
     await event_bus.publish(event_type, payload)
 
     # Create notification for instance owner (fire-and-forget)
+    # Skip intermediate "starting" notifications — only notify on terminal states
+    # (failed or successful attempts)
+    _is_starting_intermediate = event_type == "instance.started" and (
+        status or instance.status
+    ) == "starting"
+    if _is_starting_intermediate:
+        return
+
     severity = "error" if event_type == "instance.error" else "info"
     title = _derive_title(event_type)