test(transcription): harden annotation-delete specs and e2e (#722)

- Fix a stale test title that still claimed a delete button is visible.
- Strengthen the two "never renders a delete button" contract tests
  (AnnotationShape + AnnotationLayer specs) to assert the annotation
  element has zero descendant <button> elements, not just the absence of
  the removed testid (a near-tautology now that the testid is gone).
- Harden the e2e delete test: guard countBefore > 0 so a missing seed
  fails clearly instead of asserting toHaveCount(-1), and capture the
  deleted annotation's testid to assert that specific element is gone
  (identity check) alongside the count drop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/document/annotation/AnnotationLayer.svelte.spec.ts

@@ -110,6 +110,10 @@ describe('AnnotationLayer', () => {
 		});
 
 		await expect.element(page.getByTestId('annotation-ann-1')).toBeInTheDocument();
+		// Positive control: the previously-removed testid must stay absent.
 		await expect.element(page.getByTestId('annotation-delete-ann-1')).not.toBeInTheDocument();
+		// Real invariant: the annotation must contain no clickable delete control at all.
+		const annotationEl = page.getByTestId('annotation-ann-1').element() as HTMLElement;
+		expect(annotationEl.querySelectorAll('button').length).toBe(0);
 	});
 });

frontend/src/lib/document/annotation/AnnotationLayer.svelte.test.ts

@@ -240,7 +240,7 @@ describe('AnnotationLayer', () => {
 			expect(document.querySelector('[data-testid="annotation-ann-1"]')).not.toBeNull();
 		});
 
-		it('renders without throwing when canDraw is true (delete button visible)', async () => {
+		it('renders without throwing when canDraw is true (no delete button)', async () => {
 			expect(() =>
 				render(AnnotationLayer, {
 					annotations: [annotation],

frontend/src/lib/document/annotation/AnnotationShape.svelte.spec.ts

@@ -50,7 +50,11 @@ describe('AnnotationShape', () => {
 		});
 
 		await expect.element(page.getByTestId('annotation-ann-1')).toBeInTheDocument();
+		// Positive control: the previously-removed testid must stay absent.
 		await expect.element(page.getByTestId('annotation-delete-ann-1')).not.toBeInTheDocument();
+		// Real invariant: the annotation must contain no clickable delete control at all.
+		const annotationEl = page.getByTestId('annotation-ann-1').element() as HTMLElement;
+		expect(annotationEl.querySelectorAll('button').length).toBe(0);
 	});
 
 	it('calls onDeleteRequest when Delete key is pressed on the annotation', async () => {