feat: track player relationships from NPC conversations

[JOY (JOY)]

Summary

• update closed NPC conversation side effects to add a lightweight player relationship ledger entry
• preserve idempotency by tying relationship writes to the closed conversation memory summary path
• cover the player relationship record in the Nakama runtime test

Local review

• Local code-review fallback: APPROVED
• ADR compliance: compliant with Nakama backend authority and server-side intent validation
• Security: no Unity client key path added, no LLM authority expansion, no direct model state mutation

Tests

• npm run build
• npm test
• git diff --check
• em-dash scan on changed diff

[JOY (JOY)]

Codex (@codex) review

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