feat: improve setup wizard and DDNS UX

Setup wizard (Issue 1 — UI):
- pic.ngo subdomain input now uses the same split-field style as DuckDNS:
  input + static '.pic.ngo' suffix in a flex row, availability status below

Setup wizard (Issue 2 — Caddy not regenerating after completion):
- complete_setup route now fires IDENTITY_CHANGED after a successful wizard
  submission so CaddyManager regenerates the Caddyfile immediately; users
  no longer need to press 'Renew Certificate' to start ACME

Settings — DDNS status (Issue 2 — domain status missing):
- New GET /api/ddns/status endpoint: returns registered flag, domain_name,
  public_ip (ipify with 30s cache), last_ip from heartbeat
- Settings DDNS section for pic_ngo now shows a live status row with
  color-coded dot (green=registered+current, yellow=registered+stale,
  gray=not registered), current public IP, and a Check button
- Status auto-refreshes on mount and after each successful re-registration

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

api/routes/config.py

@@ -586,6 +586,42 @@ def update_ddns_config():
         return jsonify({'error': str(e)}), 500
 
 
+_ddns_public_ip_cache: dict = {'ip': None, 'at': 0}
+
+@bp.route('/api/ddns/status', methods=['GET'])
+def ddns_status():
+    import time as _time
+    from app import config_manager
+    ddns_cfg = config_manager.configs.get('ddns', {})
+    identity = config_manager.configs.get('_identity', {})
+
+    now = _time.time()
+    if now - _ddns_public_ip_cache['at'] > 30 or not _ddns_public_ip_cache['ip']:
+        try:
+            import requests as _req
+            resp = _req.get('https://api.ipify.org', timeout=5)
+            if resp.ok:
+                _ddns_public_ip_cache['ip'] = resp.text.strip()
+                _ddns_public_ip_cache['at'] = now
+        except Exception:
+            pass
+
+    last_ip = None
+    try:
+        from app import ddns_manager as _ddns_mgr_singleton
+        last_ip = _ddns_mgr_singleton._last_ip
+    except Exception:
+        pass
+
+    registered = bool(ddns_cfg.get('token'))
+    return jsonify({
+        'registered': registered,
+        'domain_name': identity.get('domain_name', ''),
+        'public_ip': _ddns_public_ip_cache['ip'],
+        'last_ip': last_ip,
+    })
+
+
 @bp.route('/api/ddns/register', methods=['POST'])
 def ddns_register():
     """Trigger (re-)registration with the configured DDNS provider."""