fix(tests): resolve 9 CI test failures in journey-editor specs

- useBlockDragDrop: add runtime expect() alongside expectTypeOf so
  browser-mode runner counts at least one assertion
- JourneyAddBar: use exact:true on 'Hinzufügen' button — partial match
  was hitting '+ Brief hinzufügen' and '+ Zwischentext hinzufügen' too
- JourneyEditor: fix 4 issues — drop wrong not.toBeInTheDocument()
  (placeholder creates accessible name); pass title:'' in publish-disabled
  test (default was non-empty); use getByPlaceholder for interlude
  textarea to avoid 4-element strict-mode violation; exact:true for
  'Hinzufügen' button
- DocumentPickerDropdown: use .click({force:true}) on aria-disabled
  option — userEvent refuses non-enabled elements

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

frontend/src/lib/document/transcription/useBlockDragDrop.svelte.test.ts

@@ -25,6 +25,8 @@ describe('createBlockDragDrop — generic type guard', () => {
 	it('TranscriptionBlockData caller still compiles — regression guard for existing transcription editor', () => {
 		// If the generic constraint is wrong this line fails tsc --noEmit
 		expectTypeOf(createBlockDragDrop<TranscriptionBlockData>).toBeFunction();
+		// Runtime assertion so browser-mode doesn't report "no assertions"
+		expect(typeof createBlockDragDrop).toBe('function');
 	});
 });