Merge codebase-memory-exploring, codebase-memory-tracing,
codebase-memory-quality, codebase-memory-reference into single
codebase-memory skill with decision matrix, workflows, and gotchas.
Old skill directories are cleaned up automatically during install.
Factual corrections vs original PR: trace_call_path -> trace_path,
removed non-existent tools (read_file, list_directory) and edge types
(OVERRIDE, USAGE, FILE_CHANGES_WITH), removed risk_labels parameter.
Co-Authored-By: gdilla <gdilla@users.noreply.github.com>