fix(cluster): improve shard reconstruction validation and start background healing service

rust/src/cluster/healing.rs

@@ -256,6 +256,18 @@ impl HealingService {
                     }
                 };
 
+                // Verify reconstructed shards are consistent
+                if !self.erasure_coder.verify(&all_shards).unwrap_or(false) {
+                    tracing::error!(
+                        bucket = manifest.bucket,
+                        key = manifest.key,
+                        chunk = chunk.chunk_index,
+                        "Shard verification failed after reconstruction"
+                    );
+                    stats.errors += 1;
+                    continue;
+                }
+
                 // Write the missing shards to the first available local drive
                 for affected_placement in &affected {
                     let shard_idx = affected_placement.shard_index as usize;