systems-power: hoist HUD cellBottom out of inner loop

Reviewer flagged the per-iteration recomputation of cellBottom inside
drawHud's column/cell loops; the value was loop-invariant. Hoist to a
file-scope const and simplify the algebra.

systems-power

systems-power: drawHud, room dimming, right-click input

systems-power

crew-movement: wire input, tick, and render

Add drawCrew to render.go (interpolated circle + selection ring + initial label).
Extend Game with crew slice, walkable-tile map, selectedCrew, and dt-based tick;
handle left-click for crew selection and BFS-path dispatch.

scaffold game loop and placeholder ship render