feat(cli): map command (DOT output)

[berkeleynerd]

Implement mud-area map --world <world.sml> --out <map.dot>.

Behavior

• Parse world; (optionally) validate + link check first.
• Emit minimal Graphviz DOT: nodes per room labeled zone:id; edges per exit dir.
• No styling; portable output.

Acceptance

• DOT passes dot -Tpng locally; sample map generated for world_small.sml.