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/AnnotationShape.svelte

@@ -11,6 +11,8 @@ let {
 	blockNumber = undefined,
 	isFlashing = false,
 	isResizable = false,
+	showDelete = false,
+	onDeleteRequest,
 	onclick,
 	onpointerenter,
 	onpointerleave
@@ -23,11 +25,15 @@ let {
 	blockNumber?: number | undefined;
 	isFlashing?: boolean;
 	isResizable?: boolean;
+	showDelete?: boolean;
+	onDeleteRequest?: () => void;
 	onclick: () => void;
 	onpointerenter: () => void;
 	onpointerleave: () => void;
 } = $props();
 
+const deleteVisible = $derived(showDelete && (isHovered || isActive));
+
 function hexToRgba(hex: string, alpha: number): string {
 	const r = parseInt(hex.slice(1, 3), 16);
 	const g = parseInt(hex.slice(3, 5), 16);
@@ -83,6 +89,7 @@ let shapeStyle = $derived(
 	onclick={onclick}
 	onkeydown={(e) => {
 		if (e.key === 'Enter' || e.key === ' ') onclick();
+		if (e.key === 'Delete' && showDelete) onDeleteRequest?.();
 	}}
 	onpointerenter={onpointerenter}
 	onpointerleave={onpointerleave}
@@ -112,6 +119,51 @@ let shapeStyle = $derived(
 			{blockNumber}
 		</div>
 	{/if}
+	{#if deleteVisible}
+		<button
+			data-testid="annotation-delete-{annotation.id}"
+			type="button"
+			aria-label="Löschen"
+			onclick={(e) => {
+				e.stopPropagation();
+				onDeleteRequest?.();
+			}}
+			style="
+				position: absolute;
+				top: -8px;
+				right: -8px;
+				min-width: 44px;
+				min-height: 44px;
+				display: flex;
+				align-items: center;
+				justify-content: center;
+				border-radius: 50%;
+				background-color: #fff;
+				border: 1px solid var(--color-error, #e53e3e);
+				color: var(--color-error, #e53e3e);
+				cursor: pointer;
+				pointer-events: auto;
+				box-shadow: 0 1px 4px rgba(0,0,0,0.2);
+				z-index: 10;
+			"
+		>
+			<svg
+				width="16"
+				height="16"
+				viewBox="0 0 24 24"
+				fill="none"
+				stroke="currentColor"
+				stroke-width="1.5"
+				aria-hidden="true"
+			>
+				<path
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					d="M19 7l-.867 12.142A2 2 0 0116.138 21H7.862a2 2 0 01-1.995-1.858L5 7m5 4v6m4-6v6m1-10V4a1 1 0 00-1-1h-4a1 1 0 00-1 1v3M4 7h16"
+				/>
+			</svg>
+		</button>
+	{/if}
 	{#if isResizable}
 		<AnnotationEditOverlay annotation={annotation} />
 	{/if}