feat(telegram): /linkrepo, /unlinkrepo and /repos commands (5/5)

[TOMOKI977]

Summary

Last PR of the github-alerts chain. It adds the commands that link a repo to a forum topic. After this merges, alerts reach Telegram for linked repos.

• /linkrepo owner/repo:
  • Admin-only, and must run inside the topic that should receive the repo's alerts. Outside a topic it refuses with the same guidance as /datachannel.
  • Only works for repos of the team's claimed org.
  • Re-linking moves the repo, and the reply says from topic A to topic B.
• /unlinkrepo owner/repo: admin-only, inside a topic.
• /repos:
  • Read-only, for any registered team member, anywhere in the group. In a DM it uses the existing team picker.
  • The reply is capped below Telegram's 4096 characters: whole lines, then ...and N more.
• Each refusal (bad format, unclaimed org, not admin, not a member) gets its own reply through errorReplies. Anything unlisted, such as a D1 failure, still reaches the 500 boundary.

Size exception: about 520 lines. Production code is about 180 of them and tests about 200; the rest is apply-progress notes.

Review

Full review with four lenses, since these commands gate who can link what. No blocker or critical findings. The risk lens found nothing: the admin, member and claimed-org checks are enforced in the domain use cases, and names are lowercased before comparison. The warnings were fixed:

• /repos had no length cap. Past 4096 characters the reply throws, the error is unrecognized, the route answers 500, and Telegram retries the update forever. A 300-link test produced 7,689 characters and failed first.
• The re-link test now pins the exact reply, including the move direction. There is a new test for /repos with zero links.
• /linkrepo and /unlinkrepo now have separate handlers with a small shared helper, instead of one loop that branched on the command name.

A scoped fix-delta validator approved the correction, including the removal of an errorReplies entry that unlinkRepo can never throw.

Test plan

• npx vitest run: 334/334 pass
• npx tsc --noEmit: no errors

After merge

Operator steps still pending: 6.1 (GITHUB_WEBHOOK_SECRET) and 6.2 (org webhook). Then run /linkrepo inside a topic to start receiving alerts.