chore: add Justfile, apply clippy fixes, add frontend type checking

- Add Justfile with comprehensive development workflow commands (check,
lint, build, docker, etc.)
- Add @astrojs/check and typescript dependencies for frontend type
checking

frontend/src/components/Demo.tsx

@@ -69,7 +69,7 @@ const Demo = ({ class: className }: DemoProps) => {
           buildLog={buildLog}
           executables={executables}
         />
-        {downloads?.map((download, i) => (
+        {downloads?.map((download) => (
           <Badge
             key={download.token}
             className={cn(

frontend/src/components/useSocket.ts

@@ -1,5 +1,5 @@
 import { withBackend } from "@/util";
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useState } from "react";
 import useWebSocket, { ReadyState } from "react-use-websocket";
 
 export interface Download {

frontend/src/util.ts

@@ -1,4 +1,3 @@
-import { WindowIcon } from "@heroicons/react/16/solid";
 import { clsx, type ClassValue } from "clsx";
 import { twMerge } from "tailwind-merge";