Adds behavior state tracking to Mob entity with five states: idle, patrol,
converse, flee, and working. Each state has specific processing logic:
- idle: no-op (existing wander logic handles movement)
- patrol: cycles through waypoints with toroidal wrapping support
- converse: stationary during player-driven dialogue
- flee: moves away from threat coordinates
- working: stationary NPC at their post
The behavior module is self-contained and testable, ready for integration
with mob_ai.py in a later step.
