feat: add ESLint configuration and testing infrastructure

Add comprehensive ESLint setup with React and TypeScript support, create basic integration tests for the shutdown utilities, and enhance the Justfile with a new check command that runs all validation steps (cargo check, clippy, tests, and linting).

tests/basic_test.rs

@@ -0,0 +1,33 @@
+use banner::utils::shutdown::join_tasks;
+use tokio::task::JoinHandle;
+
+#[tokio::test]
+async fn test_join_tasks_success() {
+    // Create some tasks that complete successfully
+    let handles: Vec<JoinHandle<()>> = vec![
+        tokio::spawn(async { tokio::time::sleep(tokio::time::Duration::from_millis(10)).await }),
+        tokio::spawn(async { tokio::time::sleep(tokio::time::Duration::from_millis(20)).await }),
+        tokio::spawn(async { /* immediate completion */ }),
+    ];
+
+    // All tasks should complete successfully
+    let result = join_tasks(handles).await;
+    assert!(result.is_ok(), "Expected all tasks to complete successfully");
+}
+
+#[tokio::test]
+async fn test_join_tasks_with_panic() {
+    // Create some tasks, including one that panics
+    let handles: Vec<JoinHandle<()>> = vec![
+        tokio::spawn(async { tokio::time::sleep(tokio::time::Duration::from_millis(10)).await }),
+        tokio::spawn(async { panic!("intentional test panic") }),
+        tokio::spawn(async { /* immediate completion */ }),
+    ];
+
+    // Should return an error because one task panicked
+    let result = join_tasks(handles).await;
+    assert!(result.is_err(), "Expected an error when a task panics");
+
+    let error_msg = result.unwrap_err().to_string();
+    assert!(error_msg.contains("1 task(s) panicked"), "Error message should mention panicked tasks");
+}