Fix stale DNS zone after wizard completes (#8)

_bootstrap_dns runs at container start before the wizard, writing the
default cell name ('mycell') into cell.zone.  When the wizard completed
it fired IDENTITY_CHANGED for Caddy but never updated the DNS zone, so
DNS records kept showing 'mycell.cell' even after naming the cell.

After successful wizard completion, call network_manager.apply_cell_name
to rename the hostname record in the primary zone file, then reload
CoreDNS.  The empty old_name triggers auto-detection so it works even
when the zone was written with the env-var default.

Adds test_setup_route.py covering: apply_cell_name called on success,
not called on failure, 410 on repeat completion, and IDENTITY_CHANGED
publication.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/routes/setup.py

@@ -90,15 +90,19 @@ def complete_setup():
     result = sm.complete_setup(payload)
     if result.get('success'):
         try:
-            from app import config_manager, service_bus, EventType
+            from app import config_manager, service_bus, EventType, network_manager
             identity = config_manager.configs.get('_identity', {})
+            cell_name = identity.get('cell_name', '')
             service_bus.publish_event(EventType.IDENTITY_CHANGED, 'setup', {
-                'cell_name': identity.get('cell_name'),
+                'cell_name': cell_name,
                 'domain': identity.get('domain'),
                 'domain_name': identity.get('domain_name'),
                 'domain_mode': identity.get('domain_mode'),
                 'effective_domain': config_manager.get_effective_domain(),
             })
+            # Bootstrap wrote the zone with 'mycell'; rename to the real cell name.
+            if cell_name:
+                network_manager.apply_cell_name('', cell_name)
         except Exception as exc:
             logger.warning(f'Failed to publish IDENTITY_CHANGED after setup: {exc}')
     status_code = 200 if result.get('success') else 400