docs: note honest date formatter, title formatter and drift fixture

Documents DocumentTitleFormatter in the document-management C4 diagram and adds
an "honest precision display" row to the CONTRIBUTING date-handling table,
pointing at formatDocumentDate / <DocumentDate>, the shared
docs/date-label-fixtures.json drift guard, and the {@html} escaping rule.

Closes #666

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -272,6 +272,7 @@ For multipart/form-data (file uploads): bypass the typed client and use `event.f
 | Form display | German `dd.mm.yyyy` with auto-dot insertion via `handleDateInput()` |
 | Wire format | ISO 8601 via a hidden `<input type="hidden" name="documentDate" value={dateIso}>` |
 | Display | `new Intl.DateTimeFormat('de-DE', …).format(new Date(val + 'T12:00:00'))` |
+| Honest precision display | `formatDocumentDate(iso, precision, end?, raw?, locale?)` (`$lib/shared/utils/documentDate.ts`) or the `<DocumentDate>` component — renders a document date at exactly its `meta_date_precision` (MONTH → "Juni 1916", never a fabricated day). It mirrors the Java `DocumentTitleFormatter`; both are pinned to `docs/date-label-fixtures.json` so the title and UI labels can't drift. `meta_date_raw` is untrusted — render it via default escaping, never `{@html}` (a CI guard enforces this). |
 
 ### Security checklist (new endpoint)
 

docs/architecture/c4/l3-backend-3b-document-management.puml

@@ -16,7 +16,8 @@ System_Boundary(backend, "API Backend (Spring Boot)") {
     Component(tagTreeLoader, "TagTreeImporter", "Spring Component", "Upserts the tag hierarchy from canonical-tag-tree.xlsx via TagService (by canonical tag_path).")
     Component(personRegLoader, "PersonRegisterImporter", "Spring Component", "Upserts register persons from canonical-persons.xlsx via PersonService (by normalizer person_id).")
     Component(personTreeLoader, "PersonTreeImporter", "Spring Component", "Upserts tree persons + relationships from canonical-persons-tree.json via PersonService and RelationshipService.")
-    Component(docLoader, "DocumentImporter", "Spring Component", "Loads canonical-documents.xlsx: routes attribution register-first (raw cell always retained in sender_text/receiver_text), parses clean dates, keeps the S3 upload + thumbnail plumbing, and ports the path-traversal / homoglyph / absolute-path / %PDF magic-byte security guards.")
+    Component(docLoader, "DocumentImporter", "Spring Component", "Loads canonical-documents.xlsx: routes attribution register-first (raw cell always retained in sender_text/receiver_text), parses clean dates, builds an honest precision-aware title via DocumentTitleFormatter, keeps the S3 upload + thumbnail plumbing, and ports the path-traversal / homoglyph / absolute-path / %PDF magic-byte security guards.")
+    Component(titleFmt, "DocumentTitleFormatter", "Pure helper", "Formats the date label baked into an import title at exactly the data's precision (MONTH -> 'Juni 1916', never a fabricated day). Mirrors the frontend formatDocumentDate; both are pinned to docs/date-label-fixtures.json (#666).")
     Component(sheetReader, "CanonicalSheetReader", "POI helper", "Maps a canonical .xlsx by header name (no positional indices), splits pipe-delimited list columns, fails closed (IMPORT_ARTIFACT_INVALID) on a missing required header.")
     Component(minioConf, "MinioConfig", "Spring @Configuration", "Creates the S3Client and S3Presigner beans with path-style access for MinIO. Validates MinIO connectivity on startup.")
     Component(docRepo, "DocumentRepository", "Spring Data JPA", "Queries documents with Specification-based dynamic search, bidirectional conversation thread queries, full-text search with ranking and match highlighting, and transcription pipeline queue projections.")
@@ -43,6 +44,7 @@ Rel(importOrch, docLoader, "4. Loads documents")
 Rel(tagTreeLoader, sheetReader, "Reads canonical .xlsx")
 Rel(personRegLoader, sheetReader, "Reads canonical .xlsx")
 Rel(docLoader, sheetReader, "Reads canonical .xlsx")
+Rel(docLoader, titleFmt, "Builds honest title date")
 Rel(tagTreeLoader, tagSvc, "Upserts tags by source_ref")
 Rel(personRegLoader, personSvc, "Upserts persons by source_ref")
 Rel(personTreeLoader, personSvc, "Upserts persons by source_ref")