Add per-endpoint circuit breaker for downstream calls on /api/fingerprint [b#099]

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox FWC26 campaign. Circuit breaker around downstream calls made by /api/fingerprint; 503 fast on open.

Requirements and Context

• Implement per the description above
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented

Suggested Execution

1. Fork the repo and create a branch
2. Implement changes touching:
   • src/routes/fingerprint.ts
   • src/lib/circuitBreaker.ts
3. Test and commit; open a PR with Closes #<issue-number> in the body

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours

[Alimzy]

Hi! I'd like to work on this issue.

I'm a software engineer with hands-on experience in testing, debugging, and building reliable features across the stack. I'm confident I can take this on and deliver a solid, well-tested solution that follows the project's existing conventions.

I'll make sure to cover the core functionality as well as relevant edge cases to keep things reliable and regression-resistant.

Let me know if I can get started, and I'll provide updates as I progress.