fix: require PRs to reference submitted bounty issue

[vgtmy]

Summary

• Add optional expected issue validation to verifyPrOwnership.
• Require MCP and relayer submission ownership checks to verify that the PR body closes the exact bounty issue URL being submitted.
• 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.

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 (all workspace checks passed)

Fixes #108

[vercel]

@vgtmy 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.

[weilixiong]

Nice fix! I hit exactly this problem — my PR #99 (which closes issue #67 — diff-filter bug) was auto-detected as matching bounty issue #70 (FUCKING TEST) instead of the correct bounty #67. I opened issue #108 to track this bug. Looking forward to this fix landing!