labels: per-label color

Give labels a color (migration 0011 adds labels.color, server_default
'default' so existing labels keep the neutral chip). The PATCH endpoint now
updates name and/or color; note serialization carries each label's color.
Frontend: a swatch picker per label in the Edit-labels modal, colored chips
on cards + in the editor (LABEL_CHIP_CLASSES), and a color dot on each
sidebar label. Reuses the note color vocabulary. (Graph node coloring rides
this in the graph-liveliness task.)

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

frontend/src/components/AppShell.vue

@@ -8,6 +8,7 @@ import { useUiStore } from "../stores/ui";
 import CommandPalette from "./CommandPalette.vue";
 import Icon from "./Icon.vue";
 import LabelsModal from "./LabelsModal.vue";
+import { NOTE_SWATCH_CLASSES, type NoteColor } from "../notes/colors";
 
 const route = useRoute();
 const router = useRouter();
@@ -127,6 +128,10 @@ onBeforeUnmount(() => window.removeEventListener("keydown", onKeydown));
 
 const currentLabelId = computed(() => (route.name === "label" ? String(route.params.id) : null));
 
+function labelDot(color: string): string {
+  return NOTE_SWATCH_CLASSES[color as NoteColor] ?? NOTE_SWATCH_CLASSES.default;
+}
+
 function onSearch(value: string) {
   searchText.value = value;
   clearTimeout(searchTimer);
@@ -226,7 +231,11 @@ async function signOut() {
             class="nav-link"
             :class="currentLabelId === lb.id ? 'nav-link-active' : ''"
           >
-            <Icon name="tag" /> <span class="truncate">{{ lb.name }}</span>
+            <span
+              class="h-2.5 w-2.5 shrink-0 rounded-full border border-black/10 dark:border-white/15"
+              :class="labelDot(lb.color)"
+            ></span>
+            <span class="truncate">{{ lb.name }}</span>
           </RouterLink>
 
           <RouterLink to="/archive" class="nav-link mt-3" :class="route.name === 'archive' ? 'nav-link-active' : ''">