feat(HAI-042): add file attachment support for tasks

- Expand MIME type support for text file uploads
- Add --attach flag to CLI task create command
- Surface attachments to triage agent with image content support
- Reference attachments in executor prompt for task execution context
- Add drag-and-drop file upload on dashboard task cards

packages/core/src/store.ts

@@ -718,6 +718,12 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
     "image/jpeg",
     "image/gif",
     "image/webp",
+    "text/plain",
+    "application/json",
+    "text/yaml",
+    "text/x-toml",
+    "text/csv",
+    "application/xml",
   ]);
 
   private static MAX_ATTACHMENT_SIZE = 5 * 1024 * 1024; // 5MB