docs(c4): add L3 frontend 3c/3d and sequence diagrams

docs/architecture/c4/seq-document-upload.puml

@@ -0,0 +1,32 @@
+@startuml
+title Document Upload Flow
+
+actor User
+participant "Frontend (SvelteKit)" as Frontend
+participant "Backend (Spring Boot)" as Backend
+participant "PermissionAspect (AOP)" as Aspect
+participant DocumentService as DocSvc
+participant FileService as FileSvc
+participant MinIO
+participant PostgreSQL as DB
+
+User -> Frontend: Submit edit form (file + metadata)
+Frontend -> Backend: PUT /api/documents/{id}\nmultipart/form-data + Authorization header
+Backend -> Aspect: @RequirePermission(WRITE_ALL) check
+Aspect -> Aspect: Verify user has WRITE_ALL authority
+Aspect --> Backend: Proceed
+Backend -> DocSvc: updateDocument(id, dto, file)
+DocSvc -> DocSvc: Resolve sender Person by ID
+DocSvc -> DocSvc: Resolve/create Tags
+DocSvc -> FileSvc: uploadFile(file, filename)
+FileSvc -> FileSvc: Generate key: documents/{UUID}_{filename}
+FileSvc -> MinIO: PutObject(bucket, key, stream)
+MinIO --> FileSvc: Success
+FileSvc --> DocSvc: S3 key
+DocSvc -> DB: UPDATE documents SET file_path=?, status='UPLOADED', ...
+DB --> DocSvc: OK
+DocSvc --> Backend: Updated Document entity
+Backend --> Frontend: 200 OK — Document JSON
+Frontend --> User: Refreshed document view
+
+@enduml