feat(replication): add typed metrics and MRF inspection

[cxymds]

Summary

• replace the untyped replication metrics passthrough with forward-compatible
  typed status and aggregate MRF contracts
• add rc bucket replication mrf ALIAS/BUCKET and expose the same command
  through the replicate compatibility surface
• preserve provider availability, cluster completeness and node counts, queue,
  latency and bandwidth scopes, runtime/durable MRF availability, and partial
  target observations
• represent legacy missing truth metadata as legacy_unknown instead of
  inferring a healthy zero backlog
• validate failed-counter consistency, negative observations, target totals,
  and response bucket identity without inventing target queues, uptime,
  per-object rows, or unavailable per-target durable records
• bound both success and error bodies to 8 MiB and retain distinct auth,
  missing configuration/bucket, unsupported, malformed, and oversized errors
• add deterministic human and output-v3 JSON projections with credential and
  control-character redaction

Compatibility

This is an additive output-v3 extension: the existing replication diff variant
and fixtures remain valid. schemas/output_v1.json and the protected command
reference are unchanged. Older server responses remain readable but are
explicitly classified as legacy_unknown where they lack truth metadata.

During a rolling RustFS upgrade, incomplete node aggregation is rendered as
partial rather than a complete healthy snapshot.

Validation

• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace --quiet
• output-v3 schema and golden fixture tests for status and MRF
• help surface verification for status, MRF, and diff commands
• seven-view review covering requirements, server contract, Rust API,
  HTTP/error bounds, security/redaction, output compatibility, and QA/operations

Dependency

The authoritative service-side truth contract is implemented by
rustfs/rustfs#5209 and rustfs/backlog#1413. Merge this PR after that dependency.

Closes rustfs/backlog#1414

Related: rustfs/backlog#1409, rustfs/backlog#1381, rustfs/backlog#1361