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/AnnotationLayer.svelte

@@ -18,7 +18,8 @@ let {
 	dimmed = false,
 	flashAnnotationId = null,
 	onDraw,
-	onAnnotationClick
+	onAnnotationClick,
+	onDeleteRequest
 }: {
 	annotations: Annotation[];
 	canDraw: boolean;
@@ -29,6 +30,7 @@ let {
 	flashAnnotationId?: string | null;
 	onDraw: (rect: DrawRect) => void;
 	onAnnotationClick?: (id: string) => void;
+	onDeleteRequest?: (annotationId: string) => void;
 } = $props();
 
 let drawStart = $state<{ x: number; y: number } | null>(null);
@@ -112,6 +114,8 @@ const containerStyle = $derived(
 			dimmed={dimmed}
 			blockNumber={blockNumbers[annotation.id]}
 			isFlashing={flashAnnotationId === annotation.id}
+			showDelete={canDraw}
+			onDeleteRequest={() => onDeleteRequest?.(annotation.id)}
 			onclick={() => onAnnotationClick?.(annotation.id)}
 			onpointerenter={() => (hoveredId = annotation.id)}
 			onpointerleave={() => (hoveredId = null)}