feat(worker): add get_effective_run_config MCP tool

Adds a read-only get_effective_run_config(taskId) tool that reports the
model/max-turns/effort/permission-mode/agent-path/system-prompt/skills a
task will actually run with, each tagged with its source (task/list/
preset/global), plus max-turns' raw requested value and clamp status.

Extracted the model/max-turns/agent-path resolution out of
TaskRunner.ResolveConfigAsync into EffectiveRunConfigResolver so the run
path and the new reporting tool share one codepath instead of risking
drift, per docs/explore-notes/worker-task-pipeline.md's max-turns trap.

tests/ClaudeDo.Worker.Tests/External/ConfigMcpToolsTests.cs

@@ -20,7 +20,7 @@ public sealed class ConfigMcpToolsTests : IDisposable
         _ctx = _db.CreateContext();
         _lists = new ListRepository(_ctx);
         _tasks = new TaskRepository(_ctx);
-        _sut = new ConfigMcpTools(_lists, _tasks, new HubBroadcaster(new CapturingHubContext()));
+        _sut = new ConfigMcpTools(_lists, _tasks, new HubBroadcaster(new CapturingHubContext()), _db.CreateFactory());
     }
 
     public void Dispose() { _ctx.Dispose(); _db.Dispose(); }