feat/upload-bar (#30)

* feat/upload-bar: add a upload bar when user upload file, indicate the upload process

* feat/save-loading-status: add save status when click back button from editor

* fix: address PR review issues in upload and save features

- Replace deprecated substr() with substring() in UploadContext
- Fix broken error handling that checked stale task status
- Fix missing useEffect dependency in UploadStatus
- Fix CSS class conflict in progress bar styling
- Add error recovery for save state in Editor (reset on failure)
- Use .finally() instead of .then() to ensure refresh on upload failure
- Fix inconsistent indentation in UploadContext

* fix e2e tests

---------

Co-authored-by: Zimeng Xiong <zxzimeng@gmail.com>

e2e/tests/drag-and-drop.spec.ts

@@ -272,11 +272,8 @@ test.describe("Drag and Drop - File Import", () => {
     const fileInput = page.locator("#dashboard-import");
     await fileInput.setInputFiles(fixturePath);
 
-    // Wait for import success modal
-    await expect(page.getByText("Import Successful")).toBeVisible({ timeout: 10000 });
-
-    // Dismiss the modal
-    await page.getByRole("button", { name: "OK" }).click();
+    // Wait for upload to complete - the UploadStatus component shows "Done" when finished
+    await expect(page.getByText("Uploads (Done)")).toBeVisible({ timeout: 10000 });
 
     // Search for the imported drawing (it uses the filename as name)
     await page.getByPlaceholder("Search drawings...").fill("small-image");