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/PdfViewer.svelte

@@ -18,6 +18,7 @@ let {
 	activeAnnotationId = $bindable<string | null>(null),
 	onAnnotationClick,
 	onTranscriptionDraw,
+	onDeleteAnnotationRequest,
 	documentFileHash,
 	annotationsDimmed = false,
 	flashAnnotationId = null
@@ -30,6 +31,7 @@ let {
 	activeAnnotationId?: string | null;
 	onAnnotationClick?: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
+	onDeleteAnnotationRequest?: (annotationId: string) => void;
 	documentFileHash?: string | null;
 	annotationsDimmed?: boolean;
 	flashAnnotationId?: string | null;
@@ -264,6 +266,7 @@ function handleAnnotationClick(id: string) {
 								flashAnnotationId={flashAnnotationId}
 								onDraw={handleDraw}
 								onAnnotationClick={handleAnnotationClick}
+								onDeleteRequest={onDeleteAnnotationRequest}
 							/>
 						{/if}
 					</div>