Cloak auras, surcoats and formations

Phase 7 of #147. Ten cloak auras (same type doesn't stack); six surcoat drills checked once a second and shown on the tactical grid: Shield Wall (full cover), Spear Hedge, Archer Line, Healer's Circle, Wedge, Lord's Colours (#77).

Done when a shield wall stops arrows for the archers behind it in a test siege.

Built by stream G (uo-combat/src/builds/auras.rs, formations.rs, tests in tests_groups.rs): every aura and drill row resolves, auras of one kind don't stack, a shield wall stops every arrow for the archer behind it, a hedge strikes whoever steps into its reach. Left: the formations on the tactical grid (#145's overlay) beyond their looping effect, and a siege test at scale.