[Domain] Warn when no room zones exist

[95x8x9]

Summary

• Adds a layout validation warning when no Room zones exist.
• Message: "Agents can only be placed inside Room or Exit zones."

Related Issue

• Closed [Domain] 레이아웃 검증: Room 구역 없음 경고 추가 #150

Area

• Engine
• Domain
• Application
• Docs
• Build
• Analysis
• Chore

Architecture Check

• I kept the dependency direction application -> domain -> engine.
• I did not add Qt UI code to src/domain.
• I did not add domain or application dependencies to src/engine.
• I used src/ as the include root.

Verification

• cmake --preset windows-debug
• cmake --build --preset build-debug
• ctest --preset test-debug
• Not run (reason below)

Risks / Follow-up