fix(task-viewer): esc capture phase to prevent App.vue handler conflict

Register the Esc keydown listener in capture phase (useCapture=true) and
call stopPropagation() so App.vue's document-level handler never fires.
Without this, both handlers ran: App.vue pushed "/" and the component
pushed "/projects/:id", with non-deterministic winner. Also fixes the
blur-then-navigate issue where App.vue blurring an input caused the
component's handler to see body as the active element and navigate
immediately instead of stopping at the blur step.

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

frontend/src/views/TaskViewerView.vue

@@ -96,8 +96,12 @@ async function loadTask(id: number) {
 
 function handleKeydown(e: KeyboardEvent) {
   if (e.key !== "Escape") return;
+  e.stopPropagation(); // prevent App.vue's global handler from also firing
   const active = document.activeElement as HTMLElement | null;
-  if (active && active !== document.body) { active.blur(); return; }
+  if (active && active !== document.body) {
+    (active as HTMLElement).blur();
+    return;
+  }
   if (store.currentTask?.project_id) {
     router.push(`/projects/${store.currentTask.project_id}`);
   } else {
@@ -107,9 +111,10 @@ function handleKeydown(e: KeyboardEvent) {
 
 onMounted(() => {
   loadTask(taskId.value);
-  window.addEventListener("keydown", handleKeydown);
+  // Capture phase so this fires before App.vue's document-level handler
+  window.addEventListener("keydown", handleKeydown, true);
 });
-onUnmounted(() => window.removeEventListener("keydown", handleKeydown));
+onUnmounted(() => window.removeEventListener("keydown", handleKeydown, true));
 
 watch(() => route.params.id, (newId) => {
   if (newId) loadTask(Number(newId));