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/DocumentViewer.svelte

@@ -25,7 +25,7 @@ type Props = {
 	flashAnnotationId?: string | null;
 	onAnnotationClick: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
-	onDeleteAnnotationRequest?: (annotationId: string) => void;
+	onAnnotationFocus?: (id: string) => void;
 };
 
 let {
@@ -42,7 +42,7 @@ let {
 	flashAnnotationId = null,
 	onAnnotationClick,
 	onTranscriptionDraw,
-	onDeleteAnnotationRequest
+	onAnnotationFocus
 }: Props = $props();
 </script>
 
@@ -104,7 +104,7 @@ let {
 			flashAnnotationId={flashAnnotationId}
 			onAnnotationClick={onAnnotationClick}
 			onTranscriptionDraw={onTranscriptionDraw}
-			onDeleteAnnotationRequest={onDeleteAnnotationRequest}
+			onAnnotationFocus={onAnnotationFocus}
 			documentFileHash={doc.fileHash ?? null}
 		/>
 	{:else if fileUrl}