Random events: earthquakes, overflowing rivers, new gold veins (free games and versus, can be switched off)

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

src/settings.rs

@@ -163,6 +163,7 @@ pub struct Settings {
     pub map_w: usize, // size of new maps (64..256)
     pub map_h: usize,
     pub surface: bool, // new free games: the eastern half lies above ground (forest)
+    pub events: bool,  // random events in free games and versus matches
     // key bindings: action id -> key name
     pub keys: BTreeMap<String, String>,
 }
@@ -198,6 +199,7 @@ impl Default for Settings {
             map_w: 64,
             map_h: 64,
             surface: false,
+            events: true,
             keys: BTreeMap::new(),
         }
     }