feat: start progress-checker opportunity cycle 1

[Asheze1127]

Summary

• add apps/console as the new opportunity-branch control-plane foundation
• introduce a minimal hackathons scope seam in API, worker, and mentor console routes
• update docs to align the combined-product direction with the current opportunity cycle

What changed

• added hackathons table, default hackathon backfill, and teams.hackathon_id
• added GET /api/hackathons plus hackathon_id filtering for /api/questions, /api/progress, and /api/teams
• stopped treating Slack team_id as product team identity in the worker path, and now resolve real teams.id from Slack channel/workspace scope
• added hackathon selector UI and scope-aware error states to the mentor question/progress pages in apps/console
• clarified cycle docs and combined-product spec so the console shells vs implemented mentor flow are explicit

Verification

• cd changeHack/apps/api && go build ./...
• cd changeHack/apps/api && go test ./...
• cd changeHack/apps/worker && pnpm typecheck
• cd changeHack/apps/worker && pnpm build
• cd changeHack && pnpm --filter @hackhub/console typecheck
• cd changeHack && pnpm --filter @hackhub/console lint
• cd changeHack && pnpm --filter @hackhub/console build
• git -C changeHack diff --check

Known gap

• cd changeHack/apps/worker && pnpm lint currently fails because eslint is not installed in that package, which is a pre-existing environment issue rather than a change introduced by this slice.

This PR is intended as the user review checkpoint for the current opportunity cycle. It should not be merged to dev without review.