NavGrid Out-of-Bounds Fix

Entities outside the NavGrid’s coverage area (e.g. in dev mode at non-centre coordinates) would have their positions clamped to the grid edge, causing A-star to trace a bogus path along that edge and all enemies to drift rightward. NavGrid now detects out-of-bounds positions before running A-star and falls back to direct movement instead.

Also fixed bot defenders in dev mode patrolling toward world centre when idle; they now stand still unless there is a target.