fix(worker): escape newline/tab in CLI args

tests/ClaudeDo.Worker.Tests/Runner/ClaudeArgsBuilderTests.cs

@@ -68,4 +68,28 @@ public sealed class ClaudeArgsBuilderTests
         var args = _builder.Build(new ClaudeRunConfig(null, """Don't say "hello".""", null, null));
         Assert.Contains("--append-system-prompt", args);
     }
+
+    [Fact]
+    public void Build_quotes_system_prompt_with_newline()
+    {
+        var args = _builder.Build(new ClaudeRunConfig(
+            Model: null,
+            SystemPrompt: "line1\nline2",
+            AgentPath: null,
+            ResumeSessionId: null));
+
+        Assert.Contains("--append-system-prompt \"line1\\nline2\"", args);
+    }
+
+    [Fact]
+    public void Build_quotes_system_prompt_with_tab()
+    {
+        var args = _builder.Build(new ClaudeRunConfig(
+            Model: null,
+            SystemPrompt: "col1\tcol2",
+            AgentPath: null,
+            ResumeSessionId: null));
+
+        Assert.Contains("\"col1", args);
+    }
 }