test: use harness resource-management in outdir/outfile test

Replace tmpdirSync() with tempDir() and wrap Bun.spawn() with
"await using" to ensure proper cleanup of spawned process and
temporary directory.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/cli/Arguments.zig

@@ -1144,6 +1144,10 @@ pub fn parse(allocator: std.mem.Allocator, ctx: Command.Context, comptime cmd: C
         }
 
         if (args.option("--outdir")) |outdir| {
+            if (args.option("--outfile")) |_| {
+                Output.errGeneric("cannot use both --outdir and --outfile", .{});
+                Global.exit(1);
+            }
             if (outdir.len > 0) {
                 ctx.bundler_options.outdir = outdir;
             }

test/bundler/cli.test.ts

@@ -419,3 +419,19 @@ test("log case 2", async () => {
     "
   `);
 });
+
+test("cannot use both --outdir and --outfile", async () => {
+  using dir = tempDir("outdir-outfile-test", {
+    "input.js": 'console.log("Hello, world!");',
+  });
+
+  await using subprocess = Bun.spawn({
+    cmd: [bunExe(), "build", "--outdir=" + dir + "/out", "--outfile=" + dir + "/out.js", dir + "/input.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stderr: "pipe",
+  });
+
+  expect(await subprocess.stderr.text()).toContain("cannot use both --outdir and --outfile");
+  expect(await subprocess.exited).not.toBe(0);
+});