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>

tests/test_cell_link_dns.py

@@ -144,7 +144,7 @@ class TestApplyAllDnsRulesPassesCellLinks(unittest.TestCase):
                 cell_links=cell_links,
             )
         mock_gen.assert_called_once_with(
-            [], '/tmp/fake_Corefile', 'cell', cell_links
+            [], '/tmp/fake_Corefile', 'cell', cell_links, None
         )
 
     def test_cell_links_none_forwarded_as_none(self):
@@ -156,7 +156,7 @@ class TestApplyAllDnsRulesPassesCellLinks(unittest.TestCase):
                 domain='cell',
                 cell_links=None,
             )
-        mock_gen.assert_called_once_with([], '/tmp/fake_Corefile', 'cell', None)
+        mock_gen.assert_called_once_with([], '/tmp/fake_Corefile', 'cell', None, None)
 
     def test_reload_called_on_success(self):
         with patch.object(firewall_manager, 'generate_corefile', return_value=True), \

tests/test_logs_endpoints.py

@@ -333,12 +333,8 @@ class TestLogVerbosity(unittest.TestCase):
     def test_put_verbosity_returns_200_and_calls_set_level(self, mock_lm):
         mock_lm.get_service_levels.return_value = {'dns': 'DEBUG'}
         with tempfile.TemporaryDirectory() as tmpdir:
-            # Endpoint builds: os.path.join(os.path.dirname(__file__), 'config', 'log_levels.json')
-            # Patch dirname to return tmpdir so the full path becomes tmpdir/config/log_levels.json
-            config_dir = os.path.join(tmpdir, 'config')
-            os.makedirs(config_dir)
             with patch('app.auth_manager', MagicMock(spec=object)), \
-                 patch('app.os.path.dirname', return_value=tmpdir):
+                 patch.dict('os.environ', {'CONFIG_DIR': tmpdir}):
                 r = self.client.put(
                     '/api/logs/verbosity',
                     data=json.dumps({'dns': 'DEBUG'}),