Phase 0: add bridge fault-injection hooks

[kacy]

Summary

• add fault-injection hooks to the centralized service registry bridge so tests can skip legacy apply or skip shadow recording per operation
• add bridge tests that exercise the two one-sided failure modes
• expose bridge fault-injection counters through rollout status and Prometheus metrics

Commits

• 69b2102 Add service registry bridge fault hooks
• 9973f47 Expose bridge fault injection counters

Verification

• zig fmt on touched files
• zig build test -- --test-filter "handleMetricsPrometheus exposes service rollout metrics" timed out after 30 seconds without emitted failures