Add three new skills under skills/application-development/:

• designing-application-transactions: 18-step guide covering transaction lifetime, implicit/explicit transactions, cockroach_restart savepoint protocol, atomic SQL (CTEs, UPSERT, guarded UPDATEs), SELECT FOR UPDATE, set-based operations, follower reads, keyset pagination, prepared statements, key distribution, connection pooling, separation of concerns, 16MB transaction payload limit, session guardrails, concurrency testing, and monitoring. Includes references/ with contention queries and Prometheus metrics.

• benchmarking-transaction-patterns: fair methodology for comparing explicit multi-statement transactions vs single-statement CTE transactions under contention, with reset discipline, metric collection, and result interpretation guidance.

• designing-multi-region-applications: pattern selection guide (REGIONAL BY ROW, GLOBAL, geo-partitioned), survival goals (ZONE vs REGION failure), 8-step migration checklist from single-region to multi-region.

What does this PR do?

Related Issue

Closes #

Type of Change

• New skill
• Skill update/improvement
• Documentation update
• Infrastructure/tooling change
• Bug fix

Skill Compliance Checklist

• SKILL.md includes required frontmatter fields (name, description)
• Skill name follows naming conventions (lowercase, hyphens, gerund form preferred)
• Skill name matches directory name exactly
• Description is specific and includes "when to use" trigger keywords
• Description is max 1024 characters
• Skill is under 500 lines (or uses references/ for detailed content)
• References official CockroachDB documentation (not duplicate content)
• Includes safety guardrails for risky operations (if applicable)
• Tested with at least one AI agent (manual validation)
• No time-sensitive information (version numbers, dates, "currently")
• Directory structure follows specification (only scripts/, references/, assets/ subdirs)
• No reserved words in skill name ("anthropic", "claude")
• Local validation passes: python scripts/validate-spec.py skills/

Documentation Updates

• README.md
• CONTRIBUTING.md
• Skill SKILL.md files
• Other (specify):

Testing

Manual testing:

• Tested with AI agent (specify which one):
• Verified skill is discoverable with appropriate prompts
• Validated technical accuracy against CockroachDB docs
• Tested any scripts or commands included in the skill

Automated testing:

• Local validation script passes: python scripts/validate-spec.py skills/
• CI validation will run automatically on this PR

Additional Context

Reviewer Notes

By submitting this PR, I confirm:

• I have read the contributing guidelines
• I have followed the Agent Skills Specification
• I have tested my changes
• I am willing to address review feedback