Replace settings module with skirmish mode

Removed the settings UI and its keybinding logic, added a skirmish view
and corresponding keybindings, simplified the SettingsState to hold
skirmish configuration, updated module exports, and changed the CLI
default map height from 25 to 21. Also fixed the main menu selection
limit.

src/cli.rs

@@ -45,7 +45,7 @@ pub struct Cli {
         long,
         help = "Map height",
         value_name = "Positive integer [11; 50]",
-        default_value = "25"
+        default_value = "21"
     )]
     pub map_height: u8,
 
@@ -64,7 +64,7 @@ pub struct Cli {
         value_name = "Positive integer",
         default_value = "50"
     )]
-    pub starting_wood: u8,
+    pub starting_wood: u16,
 
     #[arg(
         long,
@@ -72,7 +72,7 @@ pub struct Cli {
         value_name = "Positive integer",
         default_value = "25"
     )]
-    pub starting_iron: u8,
+    pub starting_iron: u16,
 
     #[arg(
         long,