fix(types): export root declarations for consumers

[vitormattos]

Summary

• fix broken root type entrypoint by pointing package types and exports['.'].types to generated dist/src/index.d.ts
• bump package version to 1.1.5

Why

Consumers importing from @libresign/pdf-elements could not resolve exported types (e.g. PDFElementObject) because the published root declaration file was empty.

Validation

• npm test
• npm run build
• post-build check confirms dist/src/index.d.ts exists and matches package entrypoint