test: add CodeBounty issue 37 linkage fixture

[TJCurnutte]

Summary

Fixes #37.

Adds a deterministic CodeBounty linkage fixture for issue #37 so the bounty amount, required PR syntax, collision snapshot, and payout boundary are captured in repo-verifiable artifacts.

Changes

• Adds test-fixtures/codebounty-issue-37-bounty-linkage.json
• Adds scripts/validate-codebounty-issue-37.py
• Adds bounty-notes/issue-37-bounty-linkage.md

Validation

• python3 -m py_compile scripts/validate-codebounty-issue-37.py
• python3 scripts/validate-codebounty-issue-37.py test-fixtures/codebounty-issue-37-bounty-linkage.json
• git diff --check

Validator output:

{"issue": 37, "ok": true, "required_pr_linkage": "fixes #37", "same_scope_open_pr_count": 0, "verified_payable_at_snapshot": false, "visible_amount_usd": 50}

Collision / payout boundary

Immediately before commit/push:

• Repo: public, not archived
• Issue: open, unlocked, unassigned, labeled 💰 Bounty Available
• Open PR collision terms checked: 37, fixes #37, issue 37, issue march 14 315pm
• Exact same-scope open PR count: 0

CodeBounty visible amount: $50. The bot announcement requires a CodeBounty application for eligibility, so this PR records developer_application_required and must be treated as submitted-visible only until platform/maintainer acceptance is verified.