New MCP tool that returns the full source code of a method by name,
returning a JSON dict keyed by method signature to distinguish overloads.
Uses IntelliJ PSI APIs (PsiShortNamesCache / PsiClass.findMethodsByName +
psiMethod.text) directly — no file-text parsing needed.
Also updates initialize_toolkit workflow guidance to reference the new tool.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>