fix: enforce actor knowledge audience boundaries

[dajiaohuang]

Closes #137.

What changed

• reject player-visible ActorKnowledge backed by DM-only events across campaign_event, direct knowledge CRUD, and atomic memory_change(commit) paths
• validate effective preserved source/disclosure values on revise while retaining explicit source clearing
• make committed NPC conversations actor-visible without exposing private authority snapshots or accepted DM commitments
• align fixtures, tool descriptions, and D&D DM memory guidance with the provenance/disclosure boundary

Validation

• uv run ruff check packages/mcp/src packages/mcp/tests
• Domain suite: all passed
• MCP suite: all passed, 1 skipped
• focused audience/memory/NPC suite: 25 passed
• D&D Module Generator Skill validator passed
• UI typecheck, 9 tests, and production build passed
• independent complex gpt-5.6-luna campaign backtest pending before merge