fix(runtime): exclude globalThis from auto-serve detection (#26107)

## Summary
- When a module exports `globalThis` (e.g., `module.exports =
globalThis`), Bun's auto-serve detection incorrectly triggered because
`globalThis.fetch` is the Fetch API function
- Scripts that export globalThis (like `core-js/es/global-this.js`)
would start a development server on port 3000 instead of exiting
normally
- Added explicit check to skip auto-serve when the default export is
`globalThis` itself

Fixes #440

## Test plan
- [x] Added test case `test/regression/issue/440.test.ts` that verifies:
  - `module.exports = globalThis` does not start a server
  - `export default globalThis` does not start a server
- [x] Verified test fails with system Bun (without fix)
- [x] Verified test passes with debug build (with fix)

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

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

test/regression/issue/440.test.ts

@@ -0,0 +1,46 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
+
+test("exporting globalThis should not start a server", async () => {
+  using dir = tempDir("issue-440", {
+    "test.js": `module.exports = globalThis;`,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "test.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  // Should NOT contain server started message
+  expect(stderr).not.toContain("Started");
+  expect(stderr).not.toContain("server:");
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});
+
+test("default export of globalThis should not start a server", async () => {
+  using dir = tempDir("issue-440-esm", {
+    "test.js": `export default globalThis;`,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "test.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  // Should NOT contain server started message
+  expect(stderr).not.toContain("Started");
+  expect(stderr).not.toContain("server:");
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});