fix: require PRs to close submitted bounty issue

[Adamchaua]

Summary

• Require PR ownership verification to confirm the PR body closes/fixes/resolves the exact bounty issue being submitted.
• Pass the bounty issue URL through both MCP submit pre-checks and relayer post-checks.
• Add regression coverage for the diff-filter: ignore Anchor's .anchor/ generated directory #67 vs test: dashboard greeting shows 'Hello, undefined' for users without a name #70 mismatch case and full issue URL references.

Test Plan

• corepack pnpm --filter @ghbounty/shared test -- tests/github/verify-pr-ownership.test.ts
• corepack pnpm --filter @ghbounty/shared typecheck
• corepack pnpm --filter @ghbounty/mcp typecheck
• corepack pnpm --filter @ghbounty/relayer typecheck
• Pre-commit hook: pnpm typecheck && pnpm test passed workspace-wide

Fixes #108

[vercel]

Someone is attempting to deploy a commit to the weareghbounty-6269's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Adamchaua]

Hi maintainers — this PR is still current from my side. The change keeps the bounty workflow stricter by requiring submitted bounty PRs to close/link the corresponding issue, which should make review and payout tracking less ambiguous. The only visible blocker I see is the Vercel authorization/deployment check, not a code concern. Happy to revise the wording or validation behavior if you want a different policy edge case handled.