[Domain] infer imported layout and validation

[learncold]

Summary

• build FacilityLayout2D from imported CanonicalGeometry in the domain layer
• add import validation for missing exits, disconnected walkable areas, and narrow connections
• preserve imported obstacles as layout barriers and infer adjacency connections while respecting wall seams
• extend DXF and builder tests to cover happy path, disconnected layouts, adjacency inference, and wall-blocked seams

Related Issue

• Closes Task-build FacilityLayout2D inference and import validation for demo floor plans #55

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

• adjacency and wall-seam inference is still heuristic geometry logic, so unusually noisy floor plans may need additional normalization rules later