Harden KnowledgePack retrieval and redacted PromptTrace

[JOY]

Summary

Make NPC context compact, inspectable, and safe before expanding more dialogue features.

Scope

• Keep zone, profession, faction, quest, and private memory context as tagged KnowledgePacks.
• Retrieve only compact relevant packs per decision.
• Store redacted PromptTrace metadata: identity version, memory ids, relationship ids, knowledge pack ids, objective id, source, latency, fallback reason, and validation result.
• Avoid storing raw secrets or full prompts by default.

Acceptance Criteria

• PromptTrace can explain which context components shaped a decision without storing raw provider prompt text.
• KnowledgePack selection is bounded and relevance-scored beyond fixed MVP selectors.
• Unity debug UI can show PromptTrace summaries for the selected NPC.
• Tests cover prompt trace redaction, context caps, and missing pack fallback.

References

• docs/design/26-ai-npc-backend-client-roadmap.md
• docs/design/16-npc-society-multi-agent-architecture.md
• docs/design/25-ai-npc-research-anchor-map.md

[JOY]

Verified and merged via PR #181. KnowledgePack selection is now bounded and scored, PromptTrace records redacted selected/missing pack metadata, context scores, objective id, and identity version, and Unity debug HUD can display that metadata without raw prompts.