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/db/models.py

@@ -46,6 +46,7 @@ class Node(Base):
     width: Mapped[float | None] = mapped_column(Float, nullable=True)
     height: Mapped[float | None] = mapped_column(Float, nullable=True)
     bottom_handles: Mapped[int] = mapped_column(Integer, default=1)
+    ieee_address: Mapped[str | None] = mapped_column(String, index=True, nullable=True)
     last_seen: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     response_time_ms: Mapped[int | None] = mapped_column(Integer)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
@@ -86,7 +87,7 @@ class PendingDevice(Base):
     __tablename__ = "pending_devices"
 
     id: Mapped[str] = mapped_column(String, primary_key=True, default=_uuid)
-    ip: Mapped[str] = mapped_column(String, nullable=False)
+    ip: Mapped[str | None] = mapped_column(String, nullable=True)
     mac: Mapped[str | None] = mapped_column(String)
     hostname: Mapped[str | None] = mapped_column(String)
     os: Mapped[str | None] = mapped_column(String)
@@ -94,6 +95,31 @@ class PendingDevice(Base):
     suggested_type: Mapped[str | None] = mapped_column(String)
     status: Mapped[str] = mapped_column(String, default="pending")
     discovery_source: Mapped[str | None] = mapped_column(String)
+    ieee_address: Mapped[str | None] = mapped_column(String, index=True, nullable=True, unique=True)
+    friendly_name: Mapped[str | None] = mapped_column(String, nullable=True)
+    device_subtype: Mapped[str | None] = mapped_column(String, nullable=True)
+    model: Mapped[str | None] = mapped_column(String, nullable=True)
+    vendor: Mapped[str | None] = mapped_column(String, nullable=True)
+    lqi: Mapped[int | None] = mapped_column(Integer, nullable=True)
+    discovered_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
+
+
+class PendingDeviceLink(Base):
+    """Link between two Zigbee endpoints discovered during import.
+
+    Endpoints are addressed by IEEE (stable across re-imports). Either side may
+    already exist as a canvas Node (resolved via Node.ieee_address) or still be
+    a PendingDevice. On approval, the matching Edge is auto-created when both
+    endpoints exist as canvas Nodes.
+    """
+
+    __tablename__ = "pending_device_links"
+
+    id: Mapped[str] = mapped_column(String, primary_key=True, default=_uuid)
+    source_ieee: Mapped[str] = mapped_column(String, nullable=False, index=True)
+    target_ieee: Mapped[str] = mapped_column(String, nullable=False, index=True)
+    lqi: Mapped[int | None] = mapped_column(Integer, nullable=True)
+    discovery_source: Mapped[str] = mapped_column(String, nullable=False, default="zigbee")
     discovered_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)