fix: expose Luna module draft contracts

[dajiaohuang]

Problem

Fresh Luna callers could reach module_draft(start/get/evidence) but tools/list exposed payload as an open object, so the required Pack manifest and source-backed D&D play profile were discoverable only through runtime failures.

Solution

• publish a bounded Draft 2020-12 action contract for start, get, evidence, edit, and finalize
• describe server-issued job/module ids, the Agent-selected pack id, exact evidence receipts, complete manifest decisions, levels, advancement, pregenerated-character review, catalogs, narrative, dependencies, and confirmation
• validate each supplied Pack decision before persisting it and enforce the advertised import-job revision guard on package edits
• cover a Luna-shaped generated Markdown workflow through finalization, import, activation, and playthrough initialization

Malformed Pack edits now leave the job revision, result, and edit history unchanged.

Verification

• uv run --package sagasmith-dnd-mcp pytest packages/mcp/tests (full suite; one existing skip)
• uv run --package sagasmith-dnd pytest packages/domain/tests
• uv run --package sagasmith-dnd-mcp pytest packages/mcp/tests/test_module_draft_contract.py packages/mcp/tests/test_three_tool_authoring_mcp.py packages/mcp/tests/test_tool_contract_quality.py packages/mcp/tests/test_full_skill_parity.py (18 passed after rebasing onto latest main)
• uv run ruff check packages/domain packages/mcp
• python skills/dnd-module-generator/scripts/validate_skill.py skills/dnd-module-generator

Closes #125