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).

Justfile

@@ -1,5 +1,14 @@
 default_services := "bot,web,scraper"
 
+default:
+    just --list
+
+check:
+    cargo check
+    cargo clippy
+    cargo nextest run
+    pnpm run -C web lint
+
 # Auto-reloading frontend server
 frontend:
     pnpm run -C web dev
@@ -25,4 +34,4 @@ dev-build *ARGS='--services web --tracing pretty': build-frontend
 # Auto-reloading development build for both frontend and backend
 # Will not notice if either the frontend/backend crashes, but will generally be resistant to stopping on their own.
 [parallel]
-dev *ARGS='--services web,bot': frontend (backend ARGS)
+dev *ARGS='--services web,bot': frontend (backend ARGS)