fix: full security audit remediation — P0/P1/P2/P3 fixes + 1020 passing tests

P0 — Broken functionality:
- Fix 12+ endpoints with wrong manager method signatures (email/calendar/file/routing)
- Fix email_manager.delete_email_user() missing domain arg
- Fix cell-link DNS forwarding wiped on every peer change (generate_corefile now
  accepts cell_links param; add/remove_cell_dns_forward no longer clobber the file)
- Fix Flask SECRET_KEY regenerating on every restart (persisted to DATA_DIR)
- Fix _next_peer_ip exhaustion returning 500 instead of 409
- Fix ConfigManager Caddyfile path (/app/config-caddy/)
- Fix UI double-add and wrong-key peer bugs in Peers.jsx / WireGuard.jsx
- Remove hardcoded credentials from Dashboard.jsx

P1 — Security:
- CSRF token validation on all POST/PUT/DELETE/PATCH to /api/* (double-submit pattern)
- enforce_auth: 503 only when users file readable but empty; never bypass on IOError
- WireGuard add_cell_peer: validate pubkey, name, endpoint against strict regexes
- DNS add_cell_dns_forward: validate IP and domain; reject injection chars
- DNS zone write: realpath containment + record content validation
- iptables comment /32 suffix prevents substring match deleting wrong peer rules
- is_local_request() trusts only loopback + 172.16.0.0/12 (Docker bridge)
- POST /api/containers: volume allow-list prevents arbitrary host mounts
- file_manager: bcrypt ($2b→$2y) for WebDAV; realpath containment in delete_user
- email/calendar: stop persisting plaintext passwords in user records
- routing_manager: validate IPs, networks, and interface names
- peer_registry: write peers.json at mode 0o600
- vault_manager: Fernet key file at mode 0o600
- CORS: lock down to explicit origin list
- domain/cell_name validation: reject newline, brace, semicolon injection chars

P2 — Architecture:
- Peer add: rollback registry entry if firewall rules fail post-add
- restart_service(): base class now calls _restart_container(); email and calendar
  managers call cell-mail / cell-radicale respectively
- email/calendar managers sync user list (no passwords) to cell_config.json
- Pending-restart flag cleared only after helper subprocess exits with code 0
- docker-compose.yml: add config-caddy volume to API container

P3 — Tests (854 → 1020):
- Fill test_email_endpoints.py, test_calendar_endpoints.py,
  test_network_endpoints.py, test_routing_endpoints.py
- New: test_peer_management_update.py, test_peer_management_edge_cases.py,
  test_input_validation.py, test_enforce_auth_configured.py,
  test_cell_link_dns.py, test_logs_endpoints.py, test_cells_endpoints.py,
  test_is_local_request_per_endpoint.py, test_caddy_routing.py
- E2E conftest: skip WireGuard suite when wg-quick absent
- Update existing tests to match fixed signatures and comment formats

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

tests/test_network_manager.py

@@ -399,11 +399,13 @@ class TestCellDnsForwarding(unittest.TestCase):
         self.assertNotIn('10.1.0.1', content)
 
     @patch('subprocess.run')
-    def test_remove_nonexistent_forward_is_noop(self, _mock):
-        before = open(self.corefile).read()
-        self.nm.remove_cell_dns_forward('nonexistent.cell')
+    def test_remove_nonexistent_forward_does_not_error(self, _mock):
+        # Removing a domain that was never added must not raise and must not
+        # leave the nonexistent domain in the regenerated Corefile.
+        result = self.nm.remove_cell_dns_forward('nonexistent.cell')
         after = open(self.corefile).read()
-        self.assertEqual(before, after)
+        self.assertNotIn('nonexistent.cell', after)
+        # The Corefile is regenerated (new canonical format) — that's correct.
 
 
 if __name__ == '__main__':