fix(#2): cap domain cert cache at 64 entries

src/mitm/ca.rs

@@ -207,9 +207,12 @@ impl MitmCa {
 
         let config = Arc::new(config);
 
-        // Cache it
+        // Cache it (cap at 64 entries — in practice only ~5-10 domains are seen)
         {
             let mut cache = self.domain_cache.write().await;
+            if cache.len() >= 64 {
+                cache.clear();
+            }
             cache.insert(domain.to_string(), config.clone());
         }