Interface size setting: auto, large, medium or small on the world's pixel grid

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

src/settings.rs

@@ -148,7 +148,7 @@ pub struct Settings {
     pub outlines: bool,
     pub wall_detail: u8, // 1 low, 2 medium, 3 high
     pub max_lights: u8,  // 8, 16 or 24
-    pub ui_factor: u8,   // interface size: 0 = automatic, 1..4 = fixed integer factor
+    pub ui_factor: u8,   // interface size: 0 = automatic, 2 large, 3 medium, 4 small (interface pixels per world pixel)
     pub render_scale: u8, // old pixel-look divisor (no longer used, kept for old settings files)
     pub pixel_rows: u16,  // pixel look: rows of the world on every screen (270, 360, 480)
     pub touch_ui: u8,     // touch interface: 0 = automatic (after the first touch), 1 = on, 2 = off