Moves all tree-sitter parsing logic from ai.py into a dedicated module.
Replaces the if/elif language chain with a _LANGUAGE_HANDLERS registry
mapping language names to handler functions.
Extracted: _tool_parse_structure body, _get_ts_parser, _child_by_type,
_text, and all per-language helpers (_py_func_sig, _py_class, etc.).
ai.py retains a thin wrapper for path validation.
Public API: parse_structure(path) -> JSON string
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>