feat(mtproto): per-client ad-tags, management-API auth, and record secret sync

Catch the panel up to the mtg-multi README (v1.14.0):

- Each client can now carry its own 32-hex advertising tag overriding the
  inbound-level one. The tag lives on the client (settings JSON is the
  source of truth, clients.ad_tag is the UI projection), is rendered into
  the fork's [secret-ad-tags] section for active secrets only (mtg rejects
  a config whose override names an unknown secret), is pushed per entry
  through PUT /secrets, and is part of the reload fingerprint so a tag
  edit hot-applies without dropping connections.
- The loopback management API can replace the whole secret set, so every
  mtg process now gets a random per-process api-token; the manager sends
  it as a bearer token on PUT /secrets and GET /stats and reuses it across
  config rewrites, because mtg reads the token only at startup.
- Malformed tags are rejected at every save path and additionally dropped
  in InstanceFromInbound: one bad tag would otherwise fail the whole
  generated config and take every client of the inbound down with it.
- SyncInbound never copied a re-keyed mtproto secret into the canonical
  clients table, so the clients page and subscription links kept serving
  the old secret, which mtg then rejects. It is now guarded-copied like
  the other credentials.

internal/web/translation/es-ES.json

@@ -918,6 +918,8 @@
       "wireguardAllowedIPsHint": "Déjalo vacío para asignar automáticamente; separa las entradas con comas",
       "mtprotoSecret": "Secreto MTProto",
       "mtprotoSecretHint": "El secreto FakeTLS del cliente. Vuelve a generarlo para cambiarlo.",
+      "mtprotoAdTag": "Ad-tag (canal patrocinado)",
+      "mtprotoAdTagHint": "Etiqueta hexadecimal opcional de 32 caracteres aplicada solo a este cliente, en lugar del ad-tag compartido. Déjala vacía para usar la etiqueta compartida.",
       "reverseTag": "Etiqueta inversa",
       "reverseTagPlaceholder": "Reverse tag opcional",
       "telegramId": "ID de usuario de Telegram",