M2 checklists: note kind + items backend + editor/card UI

- Migration 0006: notes.kind ('text'|'list') + note_items (text, checked,
  position). Item API: add/update(toggle)/delete/reorder; PATCH note kind; note
  responses include kind + items[] (merged in one query alongside labels).
- notes store: kind/items on Note, setKind/addItem/updateItem/deleteItem.
- NoteChecklist component (toggle/add/edit/delete items); rendered read-only-ish
  on cards (checkboxes toggle) and editable in the editor.
- Editor: convert text<->checklist (body lines become items on convert to list).

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

@@ -3,6 +3,7 @@ import { useNotesStore } from "../stores/notes";
 import { NOTE_CARD_CLASSES, type NoteColor } from "../notes/colors";
 import type { Note } from "../stores/notes";
 import Icon from "./Icon.vue";
+import NoteChecklist from "./NoteChecklist.vue";
 
 defineProps<{ note: Note }>();
 const emit = defineEmits<{ (e: "open", note: Note): void }>();
@@ -18,9 +19,27 @@ function cardClass(color: NoteColor): string {
     class="group relative mb-4 break-inside-avoid rounded-xl border p-3 shadow-sm transition hover:shadow-md"
     :class="cardClass(note.color)"
   >
+    <!-- Checklist notes can't nest interactive controls in a <button>, so use a
+         focusable div; text notes keep a semantic button. -->
+    <template v-if="note.kind === 'list'">
+      <div
+        role="button"
+        tabindex="0"
+        class="rounded focus:outline-none focus-visible:ring-2 focus-visible:ring-brand"
+        @click="emit('open', note)"
+        @keydown.enter="emit('open', note)"
+      >
+        <h3 v-if="note.title" class="mb-1 break-words text-sm font-semibold text-neutral-900 dark:text-neutral-100">
+          {{ note.title }}
+        </h3>
+      </div>
+      <NoteChecklist class="mt-1" :note-id="note.id" :items="note.items" @click="emit('open', note)" />
+    </template>
+
     <button
+      v-else
       type="button"
-      class="block w-full cursor-text text-left focus:outline-none focus-visible:ring-2 focus-visible:ring-brand focus-visible:ring-offset-2 focus-visible:ring-offset-transparent rounded"
+      class="block w-full cursor-text rounded text-left focus:outline-none focus-visible:ring-2 focus-visible:ring-brand focus-visible:ring-offset-2 focus-visible:ring-offset-transparent"
       @click="emit('open', note)"
     >
       <h3 v-if="note.title" class="mb-1 break-words text-sm font-semibold text-neutral-900 dark:text-neutral-100">