feat(mcp): add get_task_config, continue_task; fix status enum, branchDeleted, merge-from-review

- ConfigMcpTools: add get_task_config read-back (was write-only)
- ExternalMcpService: add WaitingForChildren to ListTasks filter and GetTaskStatusValues
- ExternalMcpService: add continue_task tool wrapping QueueService.ContinueTask
- ExternalMcpService: add allowWaitingForReview param to merge_task (default false)
- ExternalMcpService: fix CleanupTaskWorktree branchDeleted — now uses real branch-delete outcome
- WorktreeMaintenanceService: TryRemoveAsync returns (Removed, BranchDeleted) tuple; ForceRemoveResult gains BranchDeleted field
- Tests: 9 new cases covering all five changes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/External/ConfigMcpTools.cs

@@ -61,4 +61,14 @@ public sealed class ConfigMcpTools
         await _tasks.UpdateAgentSettingsAsync(taskId, model.NullIfBlank(), systemPrompt.NullIfBlank(), agentPath.NullIfBlank(), maxTurns, cancellationToken);
         await _broadcaster.TaskUpdated(taskId);
     }
+
+    [McpServerTool, Description("Get per-task config overrides (model/system prompt/agent path/max turns). Returns null if no override is set on this task.")]
+    public async Task<TaskConfigDto?> GetTaskConfig(string taskId, CancellationToken cancellationToken)
+    {
+        var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
+            ?? throw new InvalidOperationException($"Task {taskId} not found.");
+        if (task.Model is null && task.SystemPrompt is null && task.AgentPath is null && task.MaxTurns is null)
+            return null;
+        return new TaskConfigDto(task.Model, task.SystemPrompt, task.AgentPath, task.MaxTurns);
+    }
 }