BREAKING CHANGE(*): remove markdown-pdf, docx & slate packages

[mttrbrts]

As per the 2025 plan this PR removes support for PDF, DOCX and Slate as transformation sources and targets. These projects were not maintained, and carry heavy-weight dependencies on third-party libraries.

For PDF & DOCS, it is recommended that the same capability is achieved using tools like Docling.

For Slate, client applications should create custom transforms for newer versions of Slate or other rich-text editors.

Changes

Deletes the following packages:

• @accordproject/markdown-pdf
• @accordproject/markdown-docx
• @accordproject/markdown-slate

Flags

• Note that the graph of transformations is now split into two separate subgraphs. This is expected, as the edge from templatemark to ciceromark is available via the draft command in the template-engine.
• The deleted packages in npmjs will shortly be marked as archived too.
• The build is failing for unrelated reasons. We should address that separately.

Author Checklist

• [x] Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• [x] Vital features and changes captured in unit and/or integration tests
• [x] Commits messages follow AP format
• [ ] Extend the documentation, if necessary
• [x] Merging to main from fork:branchname