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-'

wrangler.jsonc

@@ -1,7 +1,7 @@
 {
 	"name": "webhooker",
 	"main": ".output/server/index.mjs",
-	"compatibility_date": "2026-",
+	"compatibility_date": "2026-08-04",
 	"compatibility_flags": ["nodejs_compat"],
 	"build": {
 		"command": "bun run build"