Tests — Unit and e2e coverage for validation, /config, /metrics.json

[thatkookooguy]

Goal
Ensure Phase 01 features ship with sufficient automated coverage.

Acceptance criteria

• Unit: validation (happy/missing/invalid), sanitize helper (redacts deterministically)
• e2e: GET /config returns sanitized config; GET /metrics.json returns counters and increments after a proxied call
• CI green for Linux/macOS Node LTS

Notes

• Product-focused: implementation tech is intentionally unspecified
• Plan: /.cursor/plans/m-70793e-9f5a8969.plan.md (Phase 01)