Migrate from @documenso/pdf-sign and @cantoo/pdf-lib to @libpdf/core
for all PDF manipulation and signing operations. This includes:
- New signing transports for Google Cloud KMS and local certificates
- Consolidated PDF operations using libpdf API
- Added TSA (timestamp authority) helper for digital signatures
- Removed deprecated flatten and insert utilities
- Updated tests to use new PDF library
This PR is handles the changes required to support envelopes. The new
envelope editor/signing page will be hidden during release.
The core changes here is to migrate the documents and templates model to
a centralized envelopes model.
Even though Documents and Templates are removed, from the user
perspective they will still exist as we remap envelopes to documents and
templates.
