PAIDEIA MCP v0.5.3

Adds readiness diagnostics and CI for Alt local-model setup.\n\nHighlights:\n- New paideia_doctor MCP tool for install, dependency, course readiness, action prerequisite, and recommendation diagnostics.\n- New paideia-doctor console entrypoint plus scripts/doctor.py source-tree wrapper.\n- Stdio smoke now verifies paideia_doctor.\n- GitHub Actions CI runs pytest, stdio smoke, and doctor CLI.\n- README now documents venv-safe install flow for Homebrew-managed Python.\n\nVerified with:\n- python3 -m pytest -q: 41 passed\n- python3 scripts/smoke_stdio.py: 26 tools, 5 prompts, 2 resources, 16 manifest actions, doctor status, imported notes\n- paideia-doctor in a temporary venv: package_version 0.5.3