fix: DNS split-horizon in DDNS mode, service access filter, health check, verbosity persistence

- DNS (critical): add _configured_dns_params() that returns (primary_domain,
  split_horizon_zones) from config_manager so all apply_all_dns_rules() callers
  pass the correct primary zone (e.g. 'pic.ngo') and split-horizon list
  (e.g. ['pic1.pic.ngo']) instead of the FQDN as the primary — fixes
  DNS_PROBE_FINISHED_BAD_CONFIG for all external domains when on VPN

- firewall_manager: add split_horizon_zones param to apply_all_dns_rules()
  and forward it to generate_corefile()

- Peers: filter service_access list to installed services only; peers.py
  derives valid services from config_manager.get_installed_services() with
  the email→mail ID mapping; Peers.jsx fetches from /api/store/installed
  and filters the checkboxes and defaults accordingly

- Health check: fix file_manager→'files' ID mapping so files service health
  is checked when installed (was silently skipped due to 'file' vs 'files')

- Verbosity persistence: move log_levels.json from non-mounted
  /app/api/config/ to CONFIG_DIR (/app/config/) which maps to config/api/
  on the host; both load (managers.py) and save (routes/services.py) updated

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

api/routes/cells.py

@@ -145,13 +145,13 @@ def update_cell_permissions(cell_name):
 
         # Regenerate Corefile so outbound DNS changes take effect
         try:
-            from app import config_manager
-            _id = config_manager.configs.get('_identity', {})
-            domain = _id.get('domain_name') or _id.get('domain', 'cell')
+            from app import _configured_dns_params
             peers = peer_registry.list_peers()
             cell_links = cell_link_manager.list_connections()
-            firewall_manager.apply_all_dns_rules(peers, COREFILE_PATH, domain,
-                                                 cell_links=cell_links)
+            _dns_primary, _dns_szones = _configured_dns_params()
+            firewall_manager.apply_all_dns_rules(peers, COREFILE_PATH, _dns_primary,
+                                                 cell_links=cell_links,
+                                                 split_horizon_zones=_dns_szones)
         except Exception as e:
             logger.warning(f"DNS regen after permission update failed (non-fatal): {e}")