fix: improve npc yard spacing

[JOY (JOY)]

Summary

• Clamp permanent NPC patrol radius against Relay Yard spawn grid spacing so idle roaming does not collapse adjacent NPC slots.
• Reduce stable spawn jitter and pass explicit crowd-separation tuning into prototype NPC brains.
• Add spawn spacing diagnostics to the prototype spawner status/log and update ROADMAP/CHANGELOG.

Verification

• Local code-review fallback: APPROVED. Checked Unity-only scope, stable body variant assignment, no authoritative gameplay mutation, no client LLM/provider calls, and no package changes.
• npx markdownlint-cli2@0.15.0 CHANGELOG.md ROADMAP.md: pass.
• git diff --check: pass.
• Unity worktree batchmode attempted, but Package Manager failed before compile with \The path argument must be of type string. Received undefined; this appears to be a worktree package-resolution limitation, not a script compiler error. I will run Unity MCP compile and Play Mode smoke on root dev immediately after merge.

Closes #145