Deduplicate clawtributor claim requests

[fuller-stack-dev]

Summary

• Add a persistent claim_requests table with a unique (guild_id, user_id) constraint.
• Block duplicate /claim runs and duplicate OAuth callback submissions once a claim exists.
• Record accept/reject decisions against the claim record.
• Add a Bun migration test covering the unique claim constraint.

Verification

• bun run typecheck
• bun test
• git diff --check

Migration note

I could not run the remote D1 migration from this environment because Wrangler is not authenticated here and CLOUDFLARE_API_TOKEN is not set. Before deploy/release, run bun run db:apply:remote with production Cloudflare credentials.

[thewilloftheshadow]

Will fix a couple things