Surface world: grass in daylight, forests, cliffs with cave mouths; free-game and editor option

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

src/main.rs

@@ -37,6 +37,7 @@ mod sfx;
 mod tracks;
 mod traps;
 mod sound;
+mod surface;
 mod spells;
 mod touch;
 mod ui;
@@ -173,7 +174,12 @@ fn finish_rect(app: &mut App, tool: Tool, start: (i32, i32), mx: f32, my: f32) {
 }
 
 fn new_game(seed: u32, s: &Settings) -> (Game, Cam) {
-    let g = Game::new_free(seed, s.map_w, s.map_h, s.difficulty);
+    let mut g = Game::new_free(seed, s.map_w, s.map_h, s.difficulty);
+    if s.surface {
+        // the eastern half above ground: forest, paths, cave mouths
+        g.add_surface(seed, 0.5, 2 + (s.map_h / 64) as u32);
+        g.init_fog();
+    }
     let (cx, cy) = g.map.core;
     let cam = Cam::new(cx as f32 + 1.5, cy as f32 + 1.5);
     (g, cam)