fix(review): address PR #787 review blockers — db-orm diagram, C4 diagram, UUID link text

- db-orm.puml: replace geschichten_documents with journey_items, add type column to geschichten, bump schema version to V72
- l3-backend-3g-supporting.puml: update GeschichteController and GeschichteService descriptions to mention STORY/JOURNEY subtypes and JourneyItem
- geschichten/[id]/+page.svelte: replace raw UUID fallback with m.geschichten_document_link_placeholder() i18n key
- messages/{de,en,es}.json: add geschichten_document_link_placeholder translation

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

frontend/src/routes/geschichten/[id]/+page.svelte

@@ -109,7 +109,7 @@ async function handleDelete() {
 							href="/documents/{item.documentId}"
 							class="block rounded border border-line bg-surface px-4 py-3 font-serif text-base text-ink hover:bg-muted"
 						>
-							{item.note ?? item.documentId}
+							{item.note ?? m.geschichten_document_link_placeholder()}
 						</a>
 					</li>
 				{/each}