PAIDEIA MCP v0.5.1

Adds machine-readable Alt local-model orchestration support.\n\nHighlights:\n- New alt_capability_manifest tool.\n- New MCP resources: paideia://alt/manifest and paideia://alt/system-prompt.\n- Manifest covers all 16 canonical PAIDEIA actions with action-to-tool recipes.\n- Stdio smoke now verifies tools, prompts, resources, manifest, and init_course.\n\nVerified with:\n- python3 -m pytest -q: 39 passed\n- python3 scripts/smoke_stdio.py: 23 tools, 5 prompts, 2 resources, 16 manifest actions