fix(chat): make cached media load on safari

src/data/storage/chat/local_chat_db.ts

@@ -39,7 +39,10 @@ export interface LocalChatMediaRow {
   messageId: string;
   kind: ChatMediaKind;
   remoteUrl: string;
-  blob: Blob;
+  /** v3+ stores raw bytes instead of Blob to avoid iOS WebKit Blob URL issues. */
+  bytes?: ArrayBuffer;
+  /** Legacy v2 field. Read-only fallback for users who already have cached media. */
+  blob?: Blob;
   mimeType: string;
   byteSize: number;
   createdAt: number;