Replace execSync with async alternative in device-name-resolver

[cameroncooke]

Context

src/utils/device-name-resolver.ts uses execSync to call xcrun devicectl list devices, which blocks the Node.js event loop. While mitigated by a 10s timeout and 30s TTL cache, it would be cleaner to use an async alternative.

Flagged by Sentry bot on PR #325.

Recommendation

Replace execSync/readFileSync/unlinkSync with async equivalents (execFile from child_process/promises, fs.promises.readFile, fs.promises.unlink). Low priority given the MCP server's single-request-at-a-time model and the caching layer.