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/viewer/PdfViewer.svelte

@@ -20,7 +20,7 @@ let {
 	activeAnnotationId = $bindable<string | null>(null),
 	onAnnotationClick,
 	onTranscriptionDraw,
-	onDeleteAnnotationRequest,
+	onAnnotationFocus,
 	documentFileHash,
 	annotationsDimmed = false,
 	flashAnnotationId = null,
@@ -35,7 +35,7 @@ let {
 	activeAnnotationId?: string | null;
 	onAnnotationClick?: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
-	onDeleteAnnotationRequest?: (annotationId: string) => void;
+	onAnnotationFocus?: (id: string) => void;
 	documentFileHash?: string | null;
 	annotationsDimmed?: boolean;
 	flashAnnotationId?: string | null;
@@ -294,7 +294,7 @@ function handleAnnotationClick(id: string) {
 								flashAnnotationId={flashAnnotationId}
 								onDraw={handleDraw}
 								onAnnotationClick={handleAnnotationClick}
-								onDeleteRequest={onDeleteAnnotationRequest}
+								onAnnotationFocus={onAnnotationFocus}
 							/>
 						{/if}
 					</div>