feat(worker): AskUser MCP tool so a running task can ask the user mid-run

A running task can call mcp__claudedo_run__AskUser(question) to block (up to 3
min) on a human answer. PendingQuestionRegistry holds the pending question +
TaskCompletionSource; the tool broadcasts TaskQuestionAsked, awaits the answer
(WorkerHub.AnswerTaskQuestion resolves it), and returns it as the tool result —
or a 'proceed on your judgment' fallback on timeout. The run stays Running
throughout (no status/schema change). ClaudeProcess raises MCP_TOOL_TIMEOUT so
the 60s HTTP-MCP cap doesn't kill the wait; the run MCP is now wired for every
task, not just standalone ones. System prompt updated to reconcile 'unattended'.

src/ClaudeDo.Worker/Runner/PendingQuestionRegistry.cs

@@ -0,0 +1,51 @@
+using System.Collections.Concurrent;
+
+namespace ClaudeDo.Worker.Runner;
+
+public sealed record PendingQuestion(string TaskId, string QuestionId, string Question);
+
+// In-memory store of questions a running task has raised via the AskUser MCP tool and is
+// blocking on. One pending question per task (the run's process is blocked mid-tool-call,
+// so it cannot ask twice at once). Kept out of the DB on purpose: a question that outlives
+// a Worker restart is already dead (StaleTaskRecovery flips the run to Failed). Singleton.
+public sealed class PendingQuestionRegistry
+{
+    private readonly ConcurrentDictionary<string, Entry> _byTask = new();
+
+    private sealed record Entry(string QuestionId, string Question, TaskCompletionSource<string> Answer);
+
+    // Registers a question for the task and returns its id plus the awaitable answer.
+    // A second register for the same task replaces any stale entry.
+    public (string QuestionId, Task<string> Answer) Register(string taskId, string question)
+    {
+        var questionId = Guid.NewGuid().ToString("N");
+        var tcs = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        _byTask[taskId] = new Entry(questionId, question, tcs);
+        return (questionId, tcs.Task);
+    }
+
+    // Delivers the answer to a waiting question. Returns false if no matching question is
+    // pending (already answered, timed out, or stale id).
+    public bool TryAnswer(string taskId, string questionId, string answer)
+    {
+        if (_byTask.TryGetValue(taskId, out var entry)
+            && entry.QuestionId == questionId
+            && _byTask.TryRemove(taskId, out _))
+        {
+            return entry.Answer.TrySetResult(answer ?? string.Empty);
+        }
+        return false;
+    }
+
+    public PendingQuestion? Get(string taskId) =>
+        _byTask.TryGetValue(taskId, out var entry)
+            ? new PendingQuestion(taskId, entry.QuestionId, entry.Question)
+            : null;
+
+    // Drops a pending question without delivering an answer (timeout/cancel cleanup).
+    public void Remove(string taskId, string questionId)
+    {
+        if (_byTask.TryGetValue(taskId, out var entry) && entry.QuestionId == questionId)
+            _byTask.TryRemove(taskId, out _);
+    }
+}