fix: keep runtime files in mcpb packages

[he-yufeng]

Summary

Fixes #241.

This narrows the default source map excludes and keeps node_modules/.bin in packaged bundles. The old defaults could drop runtime files in two common cases:

• package directories whose names end in .map, such as Iterator.prototype.map/
• CLI shims under node_modules/.bin that packages probe at module load time

The default still excludes normal source map files such as *.js.map, *.cjs.map, *.mjs.map, *.css.map, and *.ts.map.

To verify

• yarn test test/mcpbignore.test.ts
• yarn lint
• yarn build
• git diff --check