fix(worker): normalize model alias before preset lookup, wire DefaultMaxTurns as fallback

A full model id like claude-sonnet-4-6 in list_config.model never matched any
ModelPresets row (only bare aliases did), so every run under it landed on the
hardcoded 30-turn/DefaultLevel fallback instead of the sonnet preset row -
this is what killed two autonomous tasks at the 30-turn limit.

ModelRegistry.TryNormalizeAlias (non-throwing: exact match, then substring
match against a full model id) lets ModelPresets.For resolve a full model id
to its alias's preset row. For a model that still doesn't resolve, the
hardcoded 30 is replaced by a caller-supplied fallbackMaxTurns, and TaskRunner
now passes AppSettings.DefaultMaxTurns there - so that setting has a real
effect instead of being dead, matching the direction already noted in
docs/open.md.

tests/ClaudeDo.Data.Tests/ModelPresetsTests.cs

@@ -65,6 +65,44 @@ public class ModelPresetsTests
         Assert.True(row.MaxTurns > 0);
     }
 
+    [Fact]
+    public void For_unknown_model_uses_the_supplied_fallback_max_turns_instead_of_a_hardcoded_number()
+    {
+        var row = ModelPresets.For(ModelPresets.Defaults, "some-future-model", fallbackMaxTurns: 100);
+
+        Assert.Equal(100, row.MaxTurns);
+    }
+
+    [Fact]
+    public void For_a_full_model_id_resolves_to_its_alias_preset_row_not_the_unknown_fallback()
+    {
+        var sonnetPreset = ModelPresets.For(ModelPresets.Defaults, "sonnet");
+
+        var row = ModelPresets.For(ModelPresets.Defaults, "claude-sonnet-4-6");
+
+        Assert.Equal(sonnetPreset.Effort, row.Effort);
+        Assert.Equal(sonnetPreset.MaxTurns, row.MaxTurns);
+    }
+
+    [Fact]
+    public void For_a_full_model_id_honors_a_customized_preset_row_for_its_alias()
+    {
+        var parsed = ModelPresets.Parse(ModelPresets.Serialize(new[] { new ModelPreset("sonnet", "xhigh", 77) }));
+
+        var row = ModelPresets.For(parsed, "claude-sonnet-4-6");
+
+        Assert.Equal("xhigh", row.Effort);
+        Assert.Equal(77, row.MaxTurns);
+    }
+
+    [Fact]
+    public void For_unknown_model_never_throws_and_still_starts_a_run()
+    {
+        var exception = Record.Exception(() => ModelPresets.For(ModelPresets.Defaults, "totally-unrecognized-model"));
+
+        Assert.Null(exception);
+    }
+
     [Fact]
     public void For_null_model_uses_the_default_alias()
     {