fix(cdc): fix rdkafka Header API usage

The Header struct in rdkafka 0.37.0 has public fields (key, value) and
no new() method. Update to use struct literal syntax instead.

This fixes the compilation error blocking the v0.1.0 release workflow.

crates/miroir-core/src/cdc.rs

@@ -1780,7 +1780,7 @@ impl CdcManager {
                 .payload(&payload);
 
             // Add event_id header for consumer-side deduplication
-            let headers = OwnedHeaders::new().insert(Header::new("event_id", event.event_id.as_bytes()));
+            let headers = OwnedHeaders::new().insert(Header { key: "event_id", value: Some(event.event_id.as_bytes()) });
             record = record.headers(headers);
 
             // Send with timeout