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

frontend/src/App.tsx

@@ -540,6 +540,26 @@ export default function App() {
             open={zigbeeImportOpen}
             onClose={() => setZigbeeImportOpen(false)}
             onAddToCanvas={handleZigbeeAddToCanvas}
+            onPendingImported={(coordinator) => {
+              useCanvasStore.getState().notifyScanDeviceFound()
+              if (coordinator) {
+                const exists = useCanvasStore.getState().nodes.some((n) => n.id === coordinator.id)
+                if (!exists) {
+                  addNode({
+                    id: coordinator.id,
+                    type: 'zigbee_coordinator',
+                    position: { x: 600, y: 100 },
+                    data: {
+                      label: coordinator.label,
+                      type: 'zigbee_coordinator' as NodeData['type'],
+                      status: 'unknown' as const,
+                      services: [],
+                    },
+                  })
+                  markUnsaved()
+                }
+              }
+            }}
           />
         )}