fix(journey): editor review round — labels, errors, pending state, a11y, tests

Addresses the remaining #792 review blockers and concerns in the journey
editor cluster:

- Interlude rows show 'Zwischentext' (dedicated key), not the add-button text
- All four mutation handlers route the backend ErrorCode through
  getErrorMessage (a 409 duplicate no longer says 'bitte Seite neu laden')
  and console.error their failures so client-side errors leave a trace
- Remove implements the spec'd pending state: row stays dimmed with an
  aria-live 'wird entfernt…' until the DELETE resolves; failure keeps the row
- Move announcements fire after the reorder resolves (no false 'verschoben')
- Touch targets ≥44px (remove ×, note links, create submit); focus moves to
  the new row after add, to a sensible neighbor after remove, back to × on
  confirm-cancel; drag handle is pointer-only; title/intro get aria-labels;
  publish-disabled reason is a visible hint, not a title tooltip
- Amber warning styles use new --color-warning-* tokens with dark remaps
- Blocked interlude-clear restores the draft instead of showing phantom text
- useBlockDragDrop moves to $lib/shared/hooks — geschichte no longer imports
  another domain's internals
- Test hardening: reorder-failure rollback (non-ok + reject), publish/
  unpublish/empty-warning surface, destructive confirm path, maxlength
  assertions, JourneyCreate failure path, edit-page STORY/JOURNEY branch,
  fixture factory, m.* assertions, all fixed sleeps replaced with polling

67 component tests green across 6 spec files; transcription consumer of the
moved hook re-verified (30 green).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/geschichte/JourneyAddBar.svelte

@@ -40,6 +40,7 @@ function handleInterludeCancel() {
 	<div class="flex flex-wrap gap-2">
 		<button
 			type="button"
+			data-add-document
 			onclick={() => {
 				showPicker = !showPicker;
 				showInterludeForm = false;