feat: remote health circuit breaker and S3 error diagnostics

[jleni]

Summary

• Daemon RemoteHealth circuit breaker: Suppresses repetitive S3 HEAD probe warnings after 3 consecutive failures, entering a 45s degradation window where probes are skipped and logged at debug level. Recovers automatically on next success.
• Improved S3 error messages: Captures HTTP status code from the raw SDK response before into_service_error() strips it, so Ceph/MinIO errors now show HTTP 403 instead of unhandled error.
• Warming grace period: Remote checks now wait up to 750ms for manifest prefetch to complete before falling through to HEAD probes.
• Makefile → Justfile migration: Build tasks moved to Justfile; CI workflows updated accordingly.
• kache-service planner updates: Updated planner integration in service crate.

Test plan

• Verify cargo test head_object passes (unit tests for HEAD error classification)
• Verify cargo test remote_health passes (circuit breaker unit tests)
• Verify cargo test warming passes (warming barrier tests)
• Manual: run daemon against unreachable S3 → confirm only 1 warn + circuit breaker activation instead of per-crate spam
• Manual: confirm error message includes HTTP status code (e.g. HTTP 403)