C SDK Library API:
- Implement all 43+ library functions with JSON parsing
- Add Image API (15 functions): list, get, publish, delete, lock/unlock,
  visibility, grant/revoke access, transfer, spawn, clone
- Add infrastructure helpers: count_json_array_objects, skip_json_object,
  set_last_error with thread-local storage
- Functional tests: 30/30 passing

Migration:
- Create 6 new language directories: awk, cpp, forth, lisp, objective-c, v
- Migrate all 42 un.* files to clients/*/sync/src/
- Convert root un.* files to symlinks pointing to clients/
- Add Makefiles for new languages

Files:
- clients/c/src/un.c: Full library API implementation
- clients/c/src/un.h: Image types and function declarations
- clients/c/tests/test_functional.c: API functional tests
- CLAUDE.md: Updated migration status