feat(kanban): button to stretch the board to the full window width

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -164,6 +164,8 @@ export const App: React.FC = () => {
   const [deck, setDeck] = useState<Thought[]>([]);
   const [lists, setLists] = useState<SharedList[]>([]);
   const [activeTab, setActiveTab] = useState<ActiveTab>('triage');
+  // Kanban asked for the full window width (reported by the tasks view)
+  const [tasksWide, setTasksWide] = useState(false);
   const [previousTab, setPreviousTab] = useState<ActiveTab>('triage');
   const [selectedDocId, setSelectedDocId] = useState<string | null>(null);
   const [selectedBlockId, setSelectedBlockId] = useState<string | null>(null);
@@ -1168,7 +1170,9 @@ export const App: React.FC = () => {
       {/* Main Container */}
       {/* The workspace fills the window exactly and scrolls only inside the note, never the page */}
       <main
-        className={`flex-1 max-w-6xl w-full mx-auto px-3 sm:px-4 pt-3 pb-24 ${
+        className={`flex-1 w-full mx-auto px-3 sm:px-4 pt-3 pb-24 ${
+          activeTab === 'tasks' && tasksWide ? 'lg:max-w-none lg:px-6' : 'max-w-6xl'
+        } ${
           activeTab === 'workspace' ? 'min-h-0 flex flex-col sm:pb-0' : 'sm:pb-6'
         }`}
       >
@@ -1192,6 +1196,7 @@ export const App: React.FC = () => {
                 refreshTrigger={refreshRevision}
                 initialSelectedTaskId={selectedTaskId}
                 openTasksCount={stats.tasksOpenCount}
+                onWideChange={setTasksWide}
               />
             )}