Expand State of Mind and BehaviorTendencies for NPC Frames

[JOY]

Summary

Turn NPC traits, pressure, and relationships into visible behavior controls.

Scope

• Expand FrameHeartbeat with mood, stress, fear, confidence, dominant need, current goal, last trigger, and last plan summary.
• Derive BehaviorTendencies from identity, traits, relationships, BodyTime pressure, memory, and current state.
• Use tendencies to bias talk frequency, approach distance, avoidance, greeting tone, risk tolerance, and idle action.
• Expose compact state to Unity without giving the client authority over it.

Acceptance Criteria

• Nakama returns state-of-mind fields in NPC context.
• Two NPCs with different traits can produce different tendencies under the same world snapshot.
• Unity can display state of mind and tendency summary in debug UI.
• Tests cover deterministic tendency derivation and malformed stored state fallback.

References

• docs/design/26-ai-npc-backend-client-roadmap.md
• docs/design/13-human-believable-npc-agent-model.md
• docs/ARCHITECTURE.md

[JOY]

Implementation packet added in PR #188: docs/design/45-alpha-backlog-execution-packets.md.

Use that packet as the build contract for this issue: goal, minimum data contract, Unity/backend surface, verification, and cut line. This comment does not close the issue; implementation still needs its own PR and runtime evidence where applicable.