Tests: health gating computeHealth unit and gating/bypass integration (#203 follow-up)

[mojoatomic]

Goal
Add tests to validate health gating behavior introduced in #208/#213 and tracked by #203.

Scope

• Unit tests
  • computeHealth scoring per dimension (overall/structural/semantic)
  • Threshold comparison logic (>= vs >)
  • intentOverrides handling (e.g., refactoring floors)
  • (If kept) per-file-type thresholds application
• Integration tests
  • Gate PASS when score >= thresholds
  • Gate FAIL when score < thresholds
  • Bypass via env (HEALTH_BYPASS)
  • Bypass via commit token from config
  • (Optional) enforce maxBypassPerPR if we keep that policy

Acceptance Criteria

• Unit tests cover computeHealth and threshold semantics
• Integration tests simulate CI-like runs and assert non-zero exit on FAIL
• Bypass flows are verified (env + commit token)
• Test docs updated in HEALTH-GATING.md (Testing section)

References

• Health Gating Enforcement for Context-Aware Ratchet #203 Health gating enforcement
• feat(health): config-aware health gating (telemetry + optional gate) #208 Health telemetry + optional gate
• ci: enforce health gate (remove continue-on-error; run ratchet:context normally) #213 CI enforcement (exit codes)

[mojoatomic]

#214 is complete: merged via #217.

• Added computeHealth unit tests
• Added integration tests for threshold semantics, gateOn selection, intent overrides, and bypass flows
• Extracted computeHealth util for testability

Proceeding to #215 (docs) and #216 (init --ci / reusable workflow).