fix(audio): reject ffplay spawn errors

[tylergibbs1]

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Changes being requested

Handle the asynchronous error event from the ffplay child process in playAudio().

When ffplay cannot be started—for example, when it is not installed—spawn() returns a child process and reports the failure asynchronously. Without an error listener, Node.js throws an uncaught EventEmitter error and the promise returned by playAudio() does not reject normally.

This change attaches the listener immediately after spawning and adds a regression test confirming that callers receive the original spawn error as a rejected promise.

Additional context & links

Validation:

• pnpm test — 120 suites passed, 1,463 tests passed
• pnpm lint — formatting, ESLint, type checks, package checks, and JSR publish dry run passed
• pnpm build — Node.js and Deno builds passed

Some portions of this contribution were developed with assistance from OpenAI Codex (GPT-5). The final diff and test results were reviewed locally.

[Copilot]

Pull request overview

This PR ensures playAudio() properly rejects when ffplay fails to spawn (e.g., not installed), by handling the child process’ asynchronous error event instead of allowing an uncaught EventEmitter error.

Changes:

• Attach an error event listener to the spawned ffplay process to reject the playAudio() promise on spawn failure.
• Add a regression test that simulates a spawn failure and asserts the promise rejects with the original error.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/helpers/audio.ts	Adds ffplay child-process error handling so playAudio() rejects cleanly on spawn failures.
tests/helpers/audio.test.ts	Adds a test covering async spawn failure (error event) and verifies promise rejection behavior.

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