m4: per-view error states (board / search / graph / reminders)

Each data view now catches a failed load and shows an explicit error message
with a Retry button, instead of falling through to a misleading empty state.
Pairs with the global error toast: the toast says something failed, the view
says which and offers a retry.

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

frontend/src/views/GraphView.vue

@@ -26,6 +26,7 @@ const notes = useNotesStore();
 const allNodes = ref<GNode[]>([]);
 const edges = ref<GEdge[]>([]);
 const loading = ref(true);
+const error = ref("");
 const editing = ref<Note | null>(null);
 const showAll = ref(false);
 
@@ -73,6 +74,7 @@ function fill(color: string): string {
 
 async function loadGraph() {
   loading.value = true;
+  error.value = "";
   try {
     const res = await api.get<{ nodes: { id: string; title: string; color: string }[]; edges: GEdge[] }>(
       "/api/graph",
@@ -93,6 +95,10 @@ async function loadGraph() {
       };
     });
     edges.value = res.edges;
+  } catch (e) {
+    error.value = (e as { error?: string }).error ?? "Couldn't load the graph.";
+    allNodes.value = [];
+    edges.value = [];
   } finally {
     loading.value = false;
   }
@@ -289,6 +295,18 @@ onBeforeUnmount(() => {
 
     <div v-if="loading" class="py-24 text-center text-sm text-neutral-400">Loading graph…</div>
 
+    <div v-else-if="error" class="py-24 text-center">
+      <h2 class="text-lg font-semibold text-neutral-700 dark:text-neutral-200">Couldn't load the graph</h2>
+      <p class="mt-1 text-sm text-neutral-400">{{ error }}</p>
+      <button
+        type="button"
+        class="mt-3 rounded-md border border-neutral-300 px-3 py-1.5 text-sm hover:bg-neutral-100 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand dark:border-neutral-700 dark:hover:bg-neutral-800"
+        @click="loadGraph"
+      >
+        Retry
+      </button>
+    </div>
+
     <div v-else-if="allNodes.length === 0" class="py-24 text-center">
       <h2 class="text-lg font-semibold text-neutral-700 dark:text-neutral-200">No notes yet</h2>
       <p class="mt-1 text-sm text-neutral-400">