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/messages/en.json

@@ -1037,6 +1037,7 @@
 	"geschichten_published_on": "published on {date}",
 	"geschichten_persons_section": "People in this story",
 	"geschichten_documents_section": "Referenced documents",
+	"geschichten_document_link_placeholder": "Open document",
 	"geschichten_card_heading": "Stories",
 	"geschichten_card_write_action": "+ Write a story",
 	"geschichten_card_attach_action": "+ Attach a story",