docs(plan): add coherence-fix-pack implementation plan

Referenced from the PR description; documents the 7-task fix-pack
that closes findings C1, I1, I3, I4, I5, I6, M1, M2 from the deep
coherence review of PR #22 (rename of mcp-server-python-docs to
python-docs-mcp-server).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ayhammouda