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/zh-CN.json

@@ -918,6 +918,8 @@
       "wireguardAllowedIPsHint": "留空则自动分配；多个条目用逗号分隔",
       "mtprotoSecret": "MTProto 密钥",
       "mtprotoSecretHint": "该客户端的 FakeTLS 密钥。重新生成即可更换。",
+      "mtprotoAdTag": "广告标签（赞助频道）",
+      "mtprotoAdTagHint": "可选的 32 位十六进制标签，仅对该客户端生效，覆盖共享广告标签。留空则使用共享标签。",
       "reverseTag": "反向标签",
       "reverseTagPlaceholder": "可选 Reverse tag",
       "telegramId": "Telegram 用户 ID",