Fix ASC key format detection: handle both raw PEM and base64

The secret may contain either raw PEM text (with BEGIN header) or
base64-encoded PEM. Detect format and pass appropriately to fastlane
instead of blindly base64-decoding (which corrupts raw PEM content).

mobile/fastlane/Fastfile

@@ -20,12 +20,20 @@ platform :ios do
   lane :beta do
     setup_ci
 
-    key_content = Base64.decode64(ENV["ASC_KEY_CONTENT"])
+    raw = ENV["ASC_KEY_CONTENT"]
+    if raw.include?("BEGIN")
+      key_content = raw.gsub('\n', "\n")
+      is_base64 = false
+    else
+      key_content = raw
+      is_base64 = true
+    end
+
     app_store_connect_api_key(
       key_id: ENV["ASC_KEY_ID"],
       issuer_id: ENV["ASC_ISSUER_ID"],
       key_content: key_content,
-      is_key_content_base64: false
+      is_key_content_base64: is_base64
     )
 
     match(type: "appstore", readonly: true)