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/guide/message-format.md

@@ -27,6 +27,10 @@ Commit hashes, branches, and tags render as inline code wrapped in a hyperlink (
 
 Event-specific emoji are added by the formatters; per-group `Group.emoji` (default true) strips them all when disabled. Milestone progress bars are exempt. See [Message Language](./i18n).
 
+## Forge Source Label
+
+With `Group.forgeLabel` (default false) the message footer additionally names the source forge — GitHub, the Gitea instance hostname (hyperlinked), or a plain `Custom` — so events from different forges can be told apart. See [Groups → Forge Source Label](./groups#forge-source-label).
+
 ## In-Place Updates
 
 `workflow_run` and `check_run` messages are sent once and edited in place as the run progresses (queued → running → success/failure) — no duplicate messages. Tracking uses KV `msg:*` with a stable `updateKey` per run.