feat(prompt): instruct agents to offload out-of-scope work via SuggestImprovement

tests/ClaudeDo.Data.Tests/SystemPromptTests.cs

@@ -0,0 +1,15 @@
+using ClaudeDo.Data;
+using Xunit;
+
+namespace ClaudeDo.Data.Tests;
+
+public class SystemPromptTests
+{
+    [Fact]
+    public void SystemDefault_mentions_SuggestImprovement_offload()
+    {
+        var prompt = PromptFiles.DefaultFor(PromptKind.System);
+        Assert.Contains("Out-of-scope improvements", prompt);
+        Assert.Contains("SuggestImprovement", prompt);
+    }
+}