Final missions above ground (M30, co-op M20), surface option for versus matches, docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/coop_campaign.rs

@@ -91,7 +91,7 @@ pub fn coop_campaign() -> CampaignDoc {
             waves: sp.waves.0,
             wave_limit: sp.waves.1,
             first_wave: if sp.waves.0 { sp.waves.2 } else { 300.0 },
-            gen: GenDoc { rivers: sp.gen.0, lava: sp.gen.1, forts: sp.gen.2, rivals: 0, difficulty: sp.gen.3, surface: false },
+            gen: GenDoc { rivers: sp.gen.0, lava: sp.gen.1, forts: sp.gen.2, rivals: 0, difficulty: sp.gen.3, surface: i + 1 == specs.len() },
             next: (i + 1 < specs.len()).then(|| format!("c{:02}", i + 2)),
             pos: (40.0 + (i % 5) as f32 * 220.0, 40.0 + (i / 5) as f32 * 140.0),
             ..MissionDoc::default()