fix(transcription): remove annotation canvas delete button that obscured text (#722)

The per-annotation delete button (a 44px circular control pinned to the
box's top-right) overlapped the box below and obscured the underlying
document text. It was redundant: every user-drawn annotation has a
transcription block, and the right-hand panel already offers a
non-overlapping delete per block that cascades to the annotation.

Remove the visible button and its `deleteVisible` derived. Keep the
keyboard Delete shortcut (and its `showDelete`/`onDeleteRequest`/
`deleteAnnotation` wiring) — it obscures nothing and remains a
power-user path and the only cleanup route for orphan annotations.

Tests: replace the button-render/click specs with contract tests
asserting no delete button ever renders; repoint the e2e delete flow
to the keyboard shortcut + confirm dialog.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/document/annotation/AnnotationShape.svelte

@@ -32,8 +32,6 @@ let {
 	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);
@@ -119,51 +117,6 @@ 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: 4px;
-				right: 4px;
-				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}