fix(tests): fix 2 more pre-existing vitest-browser spec failures

TranscriptionEditView: fix 4 failing tests:
- textarea → [role="textbox"] selector (editor is contenteditable, not <textarea>)
- button clicks → dispatchEvent(MouseEvent) for reliable Svelte 5 onclick with TipTap
- mentionedPersons test: init block with @mention token so deserialize() creates a
  mention node; use userEvent.type + vi.waitFor (real timers) instead of fill +
  fake timers, which prevents TipTap onUpdate from firing the debounce timer

EntityNavSection: anchor link click → add capture-phase preventDefault before
clicking to stop iframe navigation while allowing Svelte onclick handler to run

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/admin/EntityNavSection.svelte.spec.ts

@@ -134,7 +134,13 @@ describe('EntityNavSection — flyout variant', () => {
 				called = true;
 			}
 		});
-		document.querySelector<HTMLAnchorElement>('a[href="/admin/users"]')!.click();
+		const link = document.querySelector<HTMLAnchorElement>('a[href="/admin/users"]')!;
+		// Prevent the browser from navigating the test iframe to /admin/users (which
+		// would redirect to /login and kill the iframe connection).  preventDefault()
+		// on the capture phase suppresses navigation while still letting the Svelte
+		// onclick handler (onFlyoutClick) run on the bubbling phase.
+		link.addEventListener('click', (e) => e.preventDefault(), { capture: true, once: true });
+		link.click();
 		expect(called).toBe(true);
 	});
 });