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/scan.py

@@ -6,7 +6,7 @@ from pydantic import BaseModel
 
 class PendingDeviceResponse(BaseModel):
     id: str
-    ip: str
+    ip: str | None
     mac: str | None
     hostname: str | None
     os: str | None
@@ -14,6 +14,12 @@ class PendingDeviceResponse(BaseModel):
     suggested_type: str | None
     status: str
     discovery_source: str | None
+    ieee_address: str | None = None
+    friendly_name: str | None = None
+    device_subtype: str | None = None
+    model: str | None = None
+    vendor: str | None = None
+    lqi: int | None = None
     discovered_at: datetime
 
     model_config = {"from_attributes": True}