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>

frontend/src/lib/components/DocumentViewer.svelte

@@ -24,6 +24,7 @@ type Props = {
 	flashAnnotationId?: string | null;
 	onAnnotationClick: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
+	onDeleteAnnotationRequest?: (annotationId: string) => void;
 };
 
 let {
@@ -38,7 +39,8 @@ let {
 	annotationsDimmed = false,
 	flashAnnotationId = null,
 	onAnnotationClick,
-	onTranscriptionDraw
+	onTranscriptionDraw,
+	onDeleteAnnotationRequest
 }: Props = $props();
 </script>
 
@@ -98,6 +100,7 @@ let {
 			flashAnnotationId={flashAnnotationId}
 			onAnnotationClick={onAnnotationClick}
 			onTranscriptionDraw={onTranscriptionDraw}
+			onDeleteAnnotationRequest={onDeleteAnnotationRequest}
 			documentFileHash={doc.fileHash ?? null}
 		/>
 	{:else if fileUrl}