M2 labels frontend: sidebar shell + label filter, chips, picker, manage

- AppShell: persistent left sidebar (Notes · labels · Archive · Trash) + top bar
  (site name, admin Settings, sign out); BoardView now renders inside it.
- labels store (list/create/rename/delete); Note gains labels[]; notes store
  gains setLabels + label-aware reconcile + /api/notes?label= loading.
- /label/:id route → label-filtered board.
- LabelPicker (tag a note, create-on-the-fly) in the editor; label chips shown
  on cards and in the editor; LabelsModal to create/rename/delete labels.
- api client PUT; new icons (note/tag/pencil/plus/check); nav-link styles.

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

@@ -32,6 +32,15 @@ function cardClass(color: NoteColor): string {
       <p v-if="!note.title && !note.body" class="text-sm italic text-neutral-400">Empty note</p>
     </button>
 
+    <div v-if="note.labels.length" class="mt-2 flex flex-wrap gap-1">
+      <span
+        v-for="lb in note.labels"
+        :key="lb.id"
+        class="rounded-full bg-black/5 px-2 py-0.5 text-xs text-neutral-600 dark:bg-white/10 dark:text-neutral-300"
+        >{{ lb.name }}</span
+      >
+    </div>
+
     <div
       class="mt-2 flex items-center justify-end gap-0.5 opacity-0 transition focus-within:opacity-100 group-hover:opacity-100"
     >