fix: constrain NPC model targets

[JOY (JOY)]

Summary

• send explicit nearby_actors from Unity so the model sees valid NPC social targets
• include allowed_target_ids in the DOS.AI decision prompt and require exact target ids
• accept both id and actor_id in backend target checks and extract JSON objects from slightly noisy model output

Local review

• Local code-review fallback: approved, no blockers found in the scoped target-context diff
• Boundary check: Unity still calls Nakama only; Nakama still validates all model target ids before applying intent

Verification

• npm run build (backend/nakama)
• npm test (backend/nakama)
• dotnet build Unity/SecondSpawn.AI.csproj --no-restore
• dotnet build Unity/SecondSpawn.Networking.csproj --no-restore
• git diff --check
• docker restart second-spawn-nakama and /v2/rpc/secondspawn_health smoke

Notes

A context canceled log immediately after restart was caused by the active Unity Play session hitting Nakama during container restart. The server came back healthy.