keyboard: board card navigation (j/k/arrows + actions)

Focused-card selection on the board: j/k or arrows move it, Enter opens,
e archives, # pins, x trashes the focused card (actions gated off the Trash
view). The selection is a brand ring on the card; it scrolls into view and
clamps as the list/view changes. A window keydown listener on BoardView,
ignored while typing, on a button/link, or while the editor modal is open.
Added the card keys to the ? cheat-sheet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/NoteCard.vue

@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { ref, watch } from "vue";
 import { useNotesStore } from "../stores/notes";
 import { NOTE_CARD_CLASSES, type NoteColor } from "../notes/colors";
 import type { Note } from "../stores/notes";
@@ -7,7 +8,7 @@ import LinkedText from "./LinkedText.vue";
 import NoteChecklist from "./NoteChecklist.vue";
 import { formatReminder, isOverdue } from "../notes/datetime";
 
-defineProps<{ note: Note; reorderable?: boolean }>();
+const props = defineProps<{ note: Note; reorderable?: boolean; active?: boolean }>();
 const emit = defineEmits<{
   (e: "open", note: Note): void;
   (e: "dragstart", note: Note): void;
@@ -15,6 +16,15 @@ const emit = defineEmits<{
 }>();
 const notes = useNotesStore();
 
+// When this card becomes the keyboard-focused card, scroll it into view.
+const root = ref<HTMLElement | null>(null);
+watch(
+  () => props.active,
+  (a) => {
+    if (a) root.value?.scrollIntoView({ block: "nearest", behavior: "smooth" });
+  },
+);
+
 function cardClass(color: NoteColor): string {
   return NOTE_CARD_CLASSES[color] ?? NOTE_CARD_CLASSES.default;
 }
@@ -22,8 +32,9 @@ function cardClass(color: NoteColor): string {
 
 <template>
   <div
+    ref="root"
     class="group relative mb-4 break-inside-avoid rounded-xl border p-3 shadow-sm transition hover:shadow-md"
-    :class="cardClass(note.color)"
+    :class="[cardClass(note.color), active ? 'ring-2 ring-brand' : '']"
     :draggable="reorderable && !note.trashed"
     @dragstart="emit('dragstart', note)"
     @dragover.prevent