feat: editable task fields in detail panel

- Click-to-edit title and description (inline editing)
- Clickable priority selector (toggle between critical/high/medium/low)
- Clickable source selector (toggle between all sources)
- Saving indicator
- EditableText component with Escape to cancel, Enter/blur to save
- Pass token and onTaskUpdated props from App

frontend/src/App.tsx

@@ -288,7 +288,9 @@ function Dashboard() {
             handleStatusChange(id, status);
             setSelectedTask(null);
           }}
+          onTaskUpdated={refresh}
           hasToken={hasToken}
+          token={token}
         />
       )}