feat(groups): optional forge source label in message footers

- Group.forgeLabel (default off, editable per group in the console) shows the
  source forge on every message the group's routes dispatch
- Discord embed footer: forge name next to the repo + the site's favicon as
  icon_url (Gitea instance's own favicon from its origin)
- Telegram footer: hyperlinked site name (GitHub or Gitea hostname); custom
  webhooks render a plain 'Custom' label
- forgeInfo() derives branding from event.provider + repository.html_url;
  dispatch attaches it to the NeutralMessage like mentionRoleIds
- validateGroups accepts forgeLabel booleans; GroupEditor gains the toggle
- tests: forgeInfo unit, discord/telegram footer render, dispatch on/off
- docs: groups.md + message-format.md (en/zh), config.example.yaml, AGENTS.md
- fix: wrangler.jsonc compatibility_date was an incomplete '2026-'

docs/zh/guide/message-format.md

@@ -27,6 +27,10 @@
 
 事件专属表情由格式化器添加；分组级 `Group.emoji`（默认开启）关闭后会全部去除。里程碑进度条不受影响。见[消息语言](./i18n)。
 
+## 来源平台标识
+
+设置 `Group.forgeLabel`（默认关闭）后，消息底部还会标注来源平台——GitHub、Gitea 实例主机名（带超链接）或无链接的 `Custom`——便于区分来自不同 forge 的事件。见[分组 → 来源平台标识](./groups#来源平台标识)。
+
 ## 原地更新
 
 `workflow_run` 与 `check_run` 消息只发送一次，随运行进度原地编辑（queued → running → success/failure），不会重复发消息。追踪使用 KV `msg:*` 与每次运行的稳定 `updateKey`。