fix(node): exit non-zero and log error when standalone port is taken

[lx3133584]

Problem

When the port configured for @astrojs/node standalone mode is already occupied, the built server process exits with code 0 without logging any error message (#18282).

This happened because:

1. standalone() returns the server's closed promise as done, which rejects on the server's error event. server.ts started the server but never handled done, allowing the rejection to become unhandled.
2. serve-app.ts registers a process-level unhandledRejection listener that silently returns when requestContext.getStore() is undefined (i.e. outside an active request). This swallowed the rejection at boot time. Because no socket remained listening, the event loop emptied and Node exited cleanly with code 0.

Solution

1. In packages/integrations/node/src/server.ts, catch errors on startServer().done, log them, and exit with code 1.
2. In packages/integrations/node/src/serve-app.ts, log rejections occurring outside a request context and set process.exitCode = 1 rather than silently ignoring them.
3. Added a regression test in packages/integrations/node/test/standalone-error.test.ts verifying that starting a standalone server when the port is occupied exits with code 1 and logs the EADDRINUSE error.
4. Added patch changeset for @astrojs/node.

Fixes #18282

Testing

• Ran packages/integrations/node/test/standalone-error.test.ts with verified RED / GREEN mutation testing:
  • Without the fix: exited with code 0 and empty stderr.
  • With the fix: exits with code 1 and logs the EADDRINUSE error.
• Ran all existing tests in packages/integrations/node (Prerendering, Redirects, Aborted requests, etc.) to ensure no regressions.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 6c82c7f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/node	Patch

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