feat(zigbee): import to pending section with edge persistence

Coordinator auto-approves to a canvas Node; routers/end devices land in
pending_devices keyed by IEEE. Discovered parent->child edges are stored
in pending_device_links so that approving a pending device later
auto-creates the Edge once both endpoints exist as canvas Nodes.

- new POST /api/v1/zigbee/import-pending (default mode in modal)
- new pending_device_links table; ieee_address on nodes + pending_devices
- pending_devices.ip migrated to nullable (table rebuild on existing DBs)
- approve / bulk-approve return auto-created edges; sidebar pushes them
  into the canvas store with bottom -> top-t handles
- ZigbeeImportModal: radio toggle pending vs canvas; reset on close
- PendingDeviceModal: zigbee badge, IEEE/LQI/vendor/model rows, services
  hidden for zigbee
- Sidebar pending row: ZIG source badge, LQI badge, friendly_name fallback
- SearchBar: null-safe IP, also searches friendly_name and ieee_address
- Tooltip trigger uses asChild to avoid nested-button hydration error

backend/app/schemas/zigbee.py

@@ -76,3 +76,20 @@ class ZigbeeImportResponse(BaseModel):
 class ZigbeeTestConnectionResponse(BaseModel):
     connected: bool
     message: str
+
+
+class ZigbeeCoordinatorOut(BaseModel):
+    id: str
+    label: str
+    ieee_address: str
+
+
+class ZigbeeImportPendingResponse(BaseModel):
+    """Result of importing a Z2M network into the pending section."""
+
+    pending_created: int
+    pending_updated: int
+    coordinator: ZigbeeCoordinatorOut | None = None
+    coordinator_already_existed: bool = False
+    links_recorded: int
+    device_count: int