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.

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -519,7 +519,7 @@ public sealed class TaskRunner
         // The model decides the global effort/turn defaults: one preset row per model alias
         // (Settings → General). List- and task-level max-turns overrides still win.
         var model = task.Model ?? listConfig?.Model ?? global.DefaultModel;
-        var preset = Data.Models.ModelPresets.For(global.ModelPresets, model);
+        var preset = Data.Models.ModelPresets.For(global.ModelPresets, model, global.DefaultMaxTurns);
 
         return new ClaudeRunConfig(
             Model: model,