perf: avoid small own clones and intermediate Vec allocations

- Derive Copy on 6 small enums (MessageRole, TaskState, StorageKind, EmbeddingBackend, PdfIngestMode, KnowledgeEntityType)
- Change create_ingestion_payload files param from Vec<FileInfo> to &[FileInfo]
- Remove 5 intermediate Vec allocations (4 embedding serialization + 1 format_history) using write! loop
- Remove 7 unnecessary .clone() calls exposed by Copy derive

common/src/storage/store.rs

@@ -32,7 +32,7 @@ impl StorageManager {
     /// This method validates the configuration and creates the appropriate
     /// storage backend with proper initialization.
     pub async fn new(cfg: &AppConfig) -> object_store::Result<Self> {
-        let backend_kind = cfg.storage.clone();
+        let backend_kind = cfg.storage;
         let (store, local_base) = create_storage_backend(cfg).await?;
 
         Ok(Self {