feat: make Discord announcement-only

[joshchen-dev]

Summary

All planning now happens on the web. Discord only announces the result.

• Timetable post:
  • each date appears as <t:…:F>, so every reader sees their own timezone
  • each date shows N/M available and its status
  • an Open in Raidy link button goes to /app?team=<id>
  • no member mentions and no vote buttons
  • votes and date decisions still edit the post in place, through the debounced refresher
  • closed timetables keep a history footer and no buttons
• Commands: /team and /schedule and their wizards are removed. A single /raidy command replies privately with a link to your team in that server, or a sign-in link to create one.
• Old posts: buttons on timetables posted before this change reply that Raidy moved to the web, with the link.
• Sign-in from a link: /api/auth/login?team=42 carries the team through the verified OAuth state, so you land on that team after signing in. Only a positive integer is accepted, so there is no open redirect. The landing page forwards ?team.
• Removed the in-memory wizard draft store (team.Drafts, TeamDraft) and the helpers only the wizards used.
• Updated the landing, overview and schedule copy and the README to describe the web-first flow.

Release v0.0.13.

Tests

• announce_test.go:
  • local timestamps, counts and status, no mentions, and the link button URL
  • closed-history rendering
  • /raidy reply for a team in this server and for no team
  • only /raidy is registered
• TestLoginReturnsToTheLinkedTeam: valid team IDs, a missing team, and malformed or hostile values
• Playwright: signing in from /app?team=42 links to /api/auth/login?team=42
• go vet, go test ./... with TEST_DATABASE_URL, npm run check, format:check, build, and Playwright (17 passed) all pass locally.

Manual check in Discord

• Run /raidy.
• Publish a timetable and check that the post shows times in your timezone and an Open in Raidy button.
• Vote on the web and see the counts update.
• Click a button on an old post.