feat(ecstore,scanner): deliver MRF intents from error paths (HS-01)

Wire the three production delivery points, each a single non-blocking
try_send next to the existing in-memory heal paths, which stay as the
fast path:

- read.rs decode-error branch: DecodeFailure intent beside the existing
  read-repair submit, so an Urgent ECDecode request survives restarts
  even when the Low-priority read-repair request was dropped or lost.
- add_partial: PartialWrite intent, giving partial-write recovery a
  durable Normal-priority object heal across restarts.
- scanner_folder metadata-corruption classification: MetadataCorruption
  intent beside the existing High-priority scanner heal request.

All three are on error paths only: zero cost on healthy IO.

Part of backlog#1865 (option a).

Co-Authored-By: heihutu <heihutu@gmail.com>

crates/scanner/src/scanner_folder.rs

@@ -2187,6 +2187,15 @@ impl FolderScanner {
                         }
 
                         if let GetSizeFailureAction::HealMetadata { object } = failure_action {
+                            // MRF journal intent: durable High-priority Metadata
+                            // heal across restarts (HS-01); the scanner heal
+                            // request below stays as the immediate path.
+                            rustfs_common::mrf_channel::try_send_mrf_intent(
+                                rustfs_common::mrf_channel::MrfKind::MetadataCorruption,
+                                &item.bucket,
+                                &object,
+                                None,
+                            );
                             self.send_required_scanner_heal_request(
                                 PendingScannerHealKind::Object,
                                 item.bucket.clone(),