Fix DDNS registration and wizard pre-fill after installer run

DDNS registration (setup_cell.py):
- Replace pyotp dependency with stdlib TOTP (HMAC-SHA1, RFC 6238)
  pyotp is only available inside the Docker container, not on the host
  where setup_cell.py runs — registration was silently skipped every time
- OTP header still sent if generation succeeds; omitted gracefully if not

Wizard pre-fill (setup_manager + Setup.jsx):
- GET /api/setup/status now returns 'preconfigured' dict with cell_name,
  domain_mode, domain_name, and provider tokens from installer-written config
- Setup.jsx fetches status on mount and pre-fills all form state so the
  user only needs to set password, services, and timezone — not re-enter
  the identity they already configured in the bash installer
- Fails silently so wizard still works on fresh installs with no config

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

api/setup_manager.py

@@ -74,11 +74,22 @@ class SetupManager:
         return bool(self.config_manager.get_identity().get('setup_complete', False))
 
     def get_setup_status(self) -> Dict[str, Any]:
-        """Return current setup status and wizard metadata."""
+        """Return current setup status, wizard metadata, and any pre-configured identity."""
+        identity = self.config_manager.get_identity()
+        preconfigured = {
+            k: v for k, v in {
+                'cell_name':            identity.get('cell_name', ''),
+                'domain_mode':          identity.get('domain_mode', ''),
+                'domain_name':          identity.get('domain_name', ''),
+                'cloudflare_api_token': identity.get('cloudflare_api_token', ''),
+                'duckdns_token':        identity.get('duckdns_token', ''),
+            }.items() if v
+        }
         return {
             'complete': self.is_setup_complete(),
             'available_services': AVAILABLE_SERVICES,
             'available_timezones': AVAILABLE_TIMEZONES,
+            'preconfigured': preconfigured,
         }
 
     # ── validation ────────────────────────────────────────────────────────