feat(transcribe): wire keyboard shortcuts into the document panel (#327)

Attaches the transcribeShortcuts action to the document page and wires every
command to existing context setters: j/k walk the sortOrder-sorted regions
and set activeAnnotationId, e toggles read/edit, n arms a draw cue (edit
only), Delete routes to the existing confirm path, ? opens the cheatsheet,
and Esc is now owned solely by the action — the inline onMount Esc listener
is removed (decision B1). Renders ShortcutCheatsheet and a draw-armed hint.

"t" toggles the document-level KURRENT_RECOGNITION training enrollment (the
only training surface that exists; there is no per-region flag yet — see
#321) and no-ops unless a region is active. Also reconciles annotation
Delete: the shape no longer self-handles the key, with onfocus syncing the
active region so the action deletes exactly once.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -19,7 +19,7 @@ let {
 	flashAnnotationId = null,
 	onDraw,
 	onAnnotationClick,
-	onDeleteRequest
+	onAnnotationFocus
 }: {
 	annotations: Annotation[];
 	canDraw: boolean;
@@ -30,7 +30,7 @@ let {
 	flashAnnotationId?: string | null;
 	onDraw: (rect: DrawRect) => void;
 	onAnnotationClick?: (id: string) => void;
-	onDeleteRequest?: (annotationId: string) => void;
+	onAnnotationFocus?: (id: string) => void;
 } = $props();
 
 let drawStart = $state<{ x: number; y: number } | null>(null);
@@ -115,8 +115,8 @@ const containerStyle = $derived(
 			blockNumber={blockNumbers[annotation.id]}
 			isFlashing={flashAnnotationId === annotation.id}
 			showDelete={canDraw}
-			onDeleteRequest={() => onDeleteRequest?.(annotation.id)}
 			onclick={() => onAnnotationClick?.(annotation.id)}
+			onfocus={() => onAnnotationFocus?.(annotation.id)}
 			onpointerenter={() => (hoveredId = annotation.id)}
 			onpointerleave={() => (hoveredId = null)}
 		/>