Persist workspace panel open/closed state per project

Panel state is saved to localStorage as workspace_panels_{projectId} on
every toggle and restored on mount. Each project remembers its own layout
independently. Fallback guard ensures at least one panel is always open
after restore.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/WorkspaceView.vue

@@ -37,7 +37,22 @@ function _storageKey(pid: number) {
   return `workspace_conv_${pid}`;
 }
 
-// Panel collapse state
+// Panel collapse state — persisted per project
+function _panelKey(pid: number) { return `workspace_panels_${pid}`; }
+
+function _loadPanelState(pid: number) {
+  try {
+    const raw = localStorage.getItem(_panelKey(pid));
+    if (raw) {
+      const saved = JSON.parse(raw);
+      // Ensure at least one panel is open after restore
+      if (!saved.tasks && !saved.chat && !saved.notes) saved.chat = true;
+      return saved as { tasks: boolean; chat: boolean; notes: boolean };
+    }
+  } catch { /* ignore */ }
+  return { tasks: true, chat: true, notes: true };
+}
+
 const panelOpen = ref({ tasks: true, chat: true, notes: true });
 
 const gridColumns = computed(() => {
@@ -102,11 +117,11 @@ function scrollToBottom() {
 watch(() => chatStore.streamingContent, scrollToBottom);
 
 function togglePanel(panel: keyof typeof panelOpen.value) {
-  // Ensure at least one panel stays open
   const open = panelOpen.value;
   const openCount = [open.tasks, open.chat, open.notes].filter(Boolean).length;
   if (open[panel] && openCount <= 1) return;
   panelOpen.value[panel] = !panelOpen.value[panel];
+  localStorage.setItem(_panelKey(projectId.value), JSON.stringify(panelOpen.value));
 }
 
 async function sendMessage() {
@@ -156,6 +171,9 @@ function resetTextareaHeight() {
 }
 
 onMounted(async () => {
+  // Restore panel state
+  panelOpen.value = _loadPanelState(projectId.value);
+
   // Load project info
   try {
     project.value = await apiGet<Project>(`/api/projects/${projectId.value}`);