feat: add AA in headless exports

src/app.rs

@@ -847,6 +847,9 @@ impl FractalApp {
         if cli.de {
             self.de_coloring = true;
         }
+        if cli.antialias {
+            self.antialias = true;
+        }
         if cli.buddhabrot {
             self.mode = FractalMode::Buddhabrot;
         }

src/cli.rs

@@ -74,6 +74,10 @@ pub struct Cli {
     #[arg(long)]
     pub de: bool,
 
+    /// Enable 2×2 antialiasing (supersampling; ~4× slower).
+    #[arg(long)]
+    pub antialias: bool,
+
     /// Coloring palette index.
     #[arg(long, value_name = "INDEX")]
     pub palette: Option<u32>,