fix: add symlink creation for bin entries in link mode

[jxom]

Summary

When bin entries already point to output dir (e.g., ./dist/cli.js) with a corresponding .src entry, zile now creates symlinks for them during zile dev (link mode).

This allows package.json bin entries like:

"bin": {
  "vocs": "./dist/cli.js",
  "vocs.src": "./src/cli.ts"
}

to properly create dist/cli.js -> ../src/cli.ts symlink during development.