fix: handle optional dependencies/devDependencies in package.json parsing

[Copilot]

readPackageJson() assumed both dependencies and devDependencies are always present, but both fields are optional per the npm spec. Calling Object.entries() on undefined throws at runtime when either field is absent.

Changes

• readPackageJson() — Widened return type to mark both fields as optional (Record<string, string> | undefined)
• getProduction() / getDevelopment() — Added ?? {} nullish coalescing to default absent fields to empty objects

// Before — throws if dependencies/devDependencies is absent
const packageJsonDependencies: Record<string, string> =
  packageJsonContent.dependencies;
for (const [name, version] of Object.entries(packageJsonDependencies)) { ... }

// After — safely returns [] when the field is missing
const packageJsonDependencies: Record<string, string> =
  packageJsonContent.dependencies ?? {};
for (const [name, version] of Object.entries(packageJsonDependencies)) { ... }

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