feat(viewer): show delete icon on annotation for direct block deletion (#339)

Adds a trash icon button (44×44 px touch target) directly on each annotation shape in transcription mode so users can delete a block without navigating through the sidebar. Includes keyboard support (Delete key), confirm dialog via ConfirmService, prop-chain wiring through DocumentViewer → PdfViewer → AnnotationLayer → AnnotationShape, and orphaned-annotation fallback (calls DELETE /annotations/{id} when no block is linked). Backend security regression test added for deleteBlock 403 on READ_ALL.

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

backend/src/test/java/org/raddatz/familienarchiv/controller/TranscriptionBlockControllerTest.java

@@ -260,6 +260,13 @@ class TranscriptionBlockControllerTest {
                 .andExpect(status().isForbidden());
     }
 
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void deleteBlock_returns403_whenUserHasOnlyReadAllPermission() throws Exception {
+        mockMvc.perform(delete(URL_BLOCK))
+                .andExpect(status().isForbidden());
+    }
+
     @Test
     @WithMockUser(authorities = "WRITE_ALL")
     void deleteBlock_returns204_whenAuthorised() throws Exception {