fix(zigbee): revive orphaned approved devices on re-import (#167)

When a Zigbee device was approved (PendingDevice.status=approved + Node
created) and the user later deleted the canvas Node, the PendingDevice row
was left orphaned as approved. On re-import _persist_pending_import found
the existing row, refreshed its fields but left status=approved, so it
never reappeared in the Pending list (which filters status==pending) —
the import reported devices found but Pending stayed empty.

Reset such orphaned approved rows back to pending on re-import. Hidden
devices stay hidden (explicit user intent). Adds regression tests for
both revive-approved and keep-hidden paths.

ha-relevant: yes

backend/app/api/routes/zigbee.py

@@ -223,7 +223,13 @@ async def _persist_pending_import(
             pending.vendor = n.get("vendor") or pending.vendor
             if n.get("lqi") is not None:
                 pending.lqi = n.get("lqi")
-            if pending.status == "hidden":
+            if pending.status == "approved":
+                # The device was approved earlier but its canvas Node no longer
+                # exists (no Node matched the IEEE above) — it was deleted. Revive
+                # the row to "pending" so it reappears in the Pending list on
+                # re-import instead of being silently swallowed. (Issue #167)
+                pending.status = "pending"
+            elif pending.status == "hidden":
                 # Re-imported a hidden device → leave it hidden, just refresh fields.
                 pass
             pending_updated += 1