chore: improve local health check guidance

[JOY (JOY)]

Summary

• add summary verdict and per-component next_action guidance to tools/windows/check-local-health.ps1
• harden Unity compile-error detection for Windows/Unix asset paths
• filter empty PrototypeAgentBrain decision error fields from generic Unity log warnings
• document how to interpret WARN versus FAIL in Play Mode smoke handoff docs

Closes #152.

Local verification

• powershell -NoProfile -ExecutionPolicy Bypass -File tools/windows/check-local-health.ps1
• powershell -NoProfile -ExecutionPolicy Bypass -File tools/windows/check-local-health.ps1 -Json
• fake Editor.log smoke for compile-error detection and empty decision error filtering
• npx.cmd markdownlint-cli2 "CHANGELOG.md" "docs/setup/play-mode-smoke-checklist.md" "docs/setup/agent-handoff.md"
• git diff --check
• rg -n "—|–" CHANGELOG.md docs/setup/play-mode-smoke-checklist.md docs/setup/agent-handoff.md tools/windows/check-local-health.ps1

Local code review

APPROVED. Scope is read-only tooling and docs. No Unity package changes, no gameplay authority changes, no client model-provider calls, and no restart or kill behavior was added.

Notes

Running this helper from a feature worktree while the root Unity project is open correctly reports a Unity Editor WARN because the active Unity process belongs to the root project path.