AI and navigation

Not implemented. engine/ai/ is reserved.

• Decision and perception are separate from navigation.
• Nav chunks partition and stream with world cells.
• Local and dynamic nav supports moving interiors.
• Behavior tree, utility, or GOAP can share an action and task layer. None is chosen.
• Editor overlays must show perception, decisions, blackboard, paths, and cost.

Navigation is a worker-lane candidate. It must not block the frame on a cache miss; streaming rules apply. Server workers may run AI batches only where cell ownership allows. Server meshing is not that ownership model yet. See ../networking/overview.md.