feat: filter notifications to warnings/errors/ready only and add clear-all button

Notification filtering:
- lifecycle_hooks.py: only instance.error and instance.health_changed
  with status=running generate notifications. All other lifecycle events
  (created, started, stopped, restarted, deleted) are filtered out.
- health_monitor.py: only error and unhealthy states generate notifications.
  Running/recovered state no longer creates info notifications.
- _derive_title now maps instance.health_changed to "Container ready".

Clear-all button:
- Added dismiss_all() to NotificationService
- Added DELETE /notifications endpoint for bulk dismiss
- Frontend: clearAllNotifications API, clearAll in notification context,
  "Clear all" button in notification drawer alongside "Mark all as read"
- Added CSS for .notification-clear-all with danger hover state
- Updated notification-center tests

Quality gates: pytest (21 passed), vitest (11 passed)

apps/api/src/services/health_monitor.py

@@ -220,18 +220,18 @@ class HealthMonitor:
         await self._event_bus.publish(event_type, payload)
 
         # Create notification for instance owner (fire-and-forget)
+        # Only send warnings and errors; skip "recovered" info notifications.
         if new_status == "error":
             category = "instance"
             severity = "error"
             title = "Container failed"
-        else:
+        elif new_status == "unhealthy":
             category = "health"
-            if new_status == "unhealthy":
-                severity = "warning"
-                title = "Container unhealthy"
-            else:
-                severity = "info"
-                title = "Container recovered"
+            severity = "warning"
+            title = "Container unhealthy"
+        else:
+            # Running/recovered — do not notify
+            return
 
         try:
             await notification_service.create_notification(

apps/api/src/services/lifecycle_hooks.py

@@ -24,6 +24,7 @@ def _derive_title(event_type: str) -> str:
         "instance.restarted": "Container restarted",
         "instance.deleted": "Container deleted",
         "instance.error": "Container error",
+        "instance.health_changed": "Container ready",
     }
     return mapping.get(
         event_type,
@@ -31,6 +32,21 @@ def _derive_title(event_type: str) -> str:
     )
 
 
+def _should_notify(event_type: str, status: str | None) -> bool:
+    """Determine whether a lifecycle event should generate a notification.
+
+    Only warnings, errors, and "container is ready" (health_changed running)
+    are sent to users.
+    """
+    if event_type == "instance.error":
+        return True
+    if event_type == "instance.health_changed" and status == "running":
+        return True
+    # Filter out: created, started, stopped, restarted, deleted, and any
+    # health_changed that is not "running" (unhealthy is handled by health_monitor)
+    return False
+
+
 def _build_payload(
     event_type: str,
     instance: ToolInstance,
@@ -118,15 +134,16 @@ 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:
+    # Only send warnings, errors, and "container is ready" notifications.
+    effective_status = status or instance.status
+    if not _should_notify(event_type, effective_status):
         return
 
-    severity = "error" if event_type == "instance.error" else "info"
+    severity = (
+        "error"
+        if event_type == "instance.error"
+        else "success"
+    )
     title = _derive_title(event_type)
 
     try:

apps/api/src/services/notification_service.py

@@ -195,6 +195,32 @@ class NotificationService:
         await session.commit()
         return result.rowcount or 0
 
+    async def dismiss_all(
+        self,
+        session: AsyncSession,
+        user_id: uuid.UUID,
+    ) -> int:
+        """Soft-delete all non-dismissed notifications for a user.
+
+        Args:
+            session: Database session.
+            user_id: Owner of the notifications.
+
+        Returns:
+            Number of rows updated.
+        """
+        stmt = (
+            update(Notification)
+            .where(
+                Notification.user_id == user_id,
+                Notification.dismissed_at.is_(None),
+            )
+            .values(dismissed_at=datetime.now(timezone.utc))
+        )
+        result: CursorResult[Any] = await session.execute(stmt)  # type: ignore[assignment]
+        await session.commit()
+        return result.rowcount or 0
+
     async def dismiss(
         self,
         session: AsyncSession,