feat: implement 'not_started' task status with validation and UI updates

src/app/api/project-tasks/[id]/route.js

@@ -49,6 +49,14 @@ async function updateProjectTaskStatusHandler(req, { params }) {
 			);
 		}
 
+		const allowedStatuses = ['not_started', 'pending', 'in_progress', 'completed', 'cancelled'];
+		if (!allowedStatuses.includes(status)) {
+			return NextResponse.json(
+				{ error: "Invalid status. Must be one of: " + allowedStatuses.join(', ') },
+				{ status: 400 }
+			);
+		}
+
 		updateProjectTaskStatus(id, status, req.user?.id || null);
 		return NextResponse.json({ success: true });
 	} catch (error) {