Make Grosse barricades actually stop bullets

[Rxup]

Summary

• BarricadaCMBC17 / C17 / AltC17 now block bullets by default instead of letting every shot pass through.
• Shooters within 3 tiles can fire through cover; shots from farther away hit the barricade unless the cursor is on a mob sprite behind it (sniper pick).
• Hitscan uses the same cover rules, and barricades now take damage so the existing 500 HP threshold actually works.

Test plan

• Stand next to a BarricadaCMBC17 / C17 / AltC17 and shoot past it — bullets should go through.
• Stand farther than 3 tiles and shoot at the barricade (not on a mob sprite) — the shot should hit the cover, not anyone behind it.
• From range, put the cursor on a mob sprite behind cover and shoot — the shot should hit that mob.
• From range, aim near a mob behind cover without hovering their sprite — the shot should hit the cover.
• Repeat with a hitscan/energy gun.
• Confirm BarricadaRoadC17 still blocks all bullets (unchanged).
• Confirm shooting a barricade accumulates damage toward destruction.