docs(pdftract-340): add SDK Architecture epic verification note
Complete verification of SDK Architecture and Language Coverage epic.
All 21 dependencies closed, all acceptance criteria met.
Components verified:
- SDK contract spec at docs/notes/sdk-contract.md
- Shared conformance suite (32 test cases)
- Tera-template-driven code generator
- libpdftract FFI implementation
- 10 SDK implementations (Python, Rust, Node.js, Go, Java, .NET, C/C++, Ruby, PHP, Swift)
- 10 Argo workflow templates for publishing
Closes pdftract-340