fix: prevent Bun from auto-serving the CLI entrypoint

[awesamarth]

Summary

Fixes #298.

Bun automatically starts an HTTP server when an entrypoint default-exports an object with a fetch method. The CLI's default export triggers this after ordinary commands print their output, contaminating stdout and keeping the process alive.

Remove that default export while keeping cli.serve() and the explicit serve command unchanged. Include a patch changeset.

Validation

• Reproduced on Bun 1.3.14: bun packages/cli/dist/cli.js --version printed the version followed by Started development server and did not exit; Node exited normally. The patched build exits cleanly on both runtimes.
• Packed and installed the patched CLI in an isolated Bun installation. Both bunx and bunx --bun returned parseable auth-status JSON and exited normally (temporary auth storage and a fake environment token; --interval 1 skips the update check).
• Verified stdio MCP initialization and explicit HTTP serve on Node and Bun. HTTP MCP initialization succeeds; arbitrary command paths remain blocked with 404.
• Existing CLI suite: 326 tests passed. TypeScript SDK suite: 142 tests passed.
• Build, typecheck, Biome, and Go SDK formatting, module tidy, vet, and race tests passed.

No command, flag, or schema changes. This is separate from the spinner dependency fix in #312.