[levno-710]

This is a major AST usability improvement: transformations can construct and move nodes using stable local symbols, without manually maintaining scopes, numeric IDs, or reference counts.

• Replace scope-based local bindings with LocalSymbol identities and explicit global variable nodes.
• Derive scopes, references, captures, and visibility from the AST, with validation for invalid bindings.
• Migrate the parser, unparser, transformation steps, and compilation backends to the new API.
• Preserve binding identities when building native CFF wrappers and flattening VM interpreters.
• Add AST API documentation and regression coverage.
• Remove .github/README.md so GitHub displays the main README.

Breaking change: Custom transformations must use symbol-based constructors; legacy scope-plus-ID signatures and prometheus.scope have been removed.