fix: apply_cell_name regex now matches zone files with TTL field

_generate_zone_content writes records as "name TTL IN A value" but the
regex only matched "name IN A value" (no TTL), so renaming the cell
never updated the DNS hostname record. Updated regex to make TTL optional.
Also fixed the unit test zone fixture to use the actual generated format.

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

api/network_manager.py

@@ -520,8 +520,9 @@ class NetworkManager(BaseServiceManager):
                         zone_file = os.path.join(dns_data, fname)
                         with open(zone_file) as f:
                             content = f.read()
+                        # Match name with optional TTL: "name [ttl] IN A value"
                         content = re.sub(
-                            rf'^{re.escape(old_name)}(\s+IN\s+A\s+)',
+                            rf'^{re.escape(old_name)}(\s+(?:\d+\s+)?IN\s+A\s+)',
                             f'{new_name}\\1',
                             content, flags=re.MULTILINE
                         )