fix: searchable client combobox in Nova instalação

Replaces the native list with a combobox (name/code/CNPJ search, accent- and
case-insensitive, keyboard + mouse, custom dropdown, hidden client_id = the
Gerenciador's real CLIENTE.ID). The backend resolves client_id against the
active GTI_GERENCIADOR mirror and rejects free text/unknown ids. Adds
Tenant.external_cnpj (migration 0025) mirrored via the internal endpoint.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

central/app/client_sync.py

@@ -74,7 +74,7 @@ def sync_from_gerenciador(session, clients: list[dict]) -> SyncResult:
 
         if row is None:
             name = wanted_name if wanted_name not in taken_names else f"{wanted_name} ({code})"
-            row = Tenant(name=name, source=SOURCE, external_client_id=external_id, external_code=code, active=active, synced_at=now)
+            row = Tenant(name=name, source=SOURCE, external_client_id=external_id, external_code=code, external_cnpj=client.get("cnpj"), active=active, synced_at=now)
             session.add(row)
             taken_names.add(name)
             created += 1
@@ -89,6 +89,9 @@ def sync_from_gerenciador(session, clients: list[dict]) -> SyncResult:
         if row.external_code != code:
             row.external_code = code
             changed = True
+        if row.external_cnpj != client.get("cnpj"):
+            row.external_cnpj = client.get("cnpj")
+            changed = True
         if row.active != active:
             row.active = active
             changed = True