fix(admin): show disabled heal runtime state

[overtrue]

Summary

Expose the RustFS heal runtime state in admin status responses and render disabled or uninitialized states explicitly in rc admin heal status.

Changes

• Add an optional state field to HealStatus and background heal response decoding.
• Preserve legacy behavior when older servers omit state.
• Render Disabled, Uninitialized, Idle, and In Progress from the explicit runtime state.

Verification

• cargo fmt --all --check
• cargo test -p rc-core test_heal_status_default -- --nocapture
• cargo test -p rc-s3 test_background_heal_status_response_maps_to_heal_status -- --nocapture
• cargo test -p rustfs-cli test_heal_status_indicator_reports_disabled_runtime -- --nocapture

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