feat(tasks): phase 5 — ask_operator (structured question, pause, resume)

The last backend piece: when the agent hits a decision only the operator can
make, it surfaces a structured question instead of guessing or stalling.

- ask_operator(prompt, why?, options?, context_entities?): nomos-local tool
  that records a session_questions row, moves the task to awaiting_input, emits
  question.raised, and ENDS the turn (the agent loop returns after it, so the
  agent can't barrel past its own question). The prompt becomes the assistant's
  visible message so the question also shows inline in the transcript.
- Two resume paths, both close the question + emit question.answered + return
  the task to executing:
  - Panel: POST /sessions/{id}/questions/{qid}/answer → resumes the agent in the
    background with the answer injected (reusing the continuation machinery,
    refactored continueSession → resumeSession). Returns 202; the reply lands via
    message polling.
  - Chat reply: the next chat message on a task with an open question IS the
    answer — auto-closed in handleChat; the turn itself is the resume.

Verified end-to-end: forcing a decision paused the task at awaiting_input with
the structured question (prompt/why/options/entities); a panel answer resumed
the agent (it acknowledged host:strong and continued); a plain chat reply
auto-closed a second question. Cleanup + tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/nomos/agent.go

@@ -419,6 +419,22 @@ func (a *agent) chatWith(ctx context.Context, sessionID, message, systemInject s
 			})
 			messages = append(messages, openai.ToolMessage(string(resultJSON), tc.ID))
 			slog.Info("nomos: tool success", "tool", tc.Function.Name, "ms", elapsed)
+
+			// ask_operator pauses the task: the agent has posed a decision only
+			// the operator can make. End the turn here so it doesn't barrel past
+			// its own question — the answer (panel or chat reply) resumes it.
+			// The prompt becomes the assistant's visible message so the question
+			// also shows inline in the transcript.
+			if tc.Function.Name == "ask_operator" {
+				prompt, _ := args["prompt"].(string)
+				emit(agentEvent{Type: "text", Data: prompt, SessionID: sessionID})
+				emit(agentEvent{Type: "done", Data: map[string]any{
+					"session_id":     sessionID,
+					"correlation_id": correlationID,
+					"iteration":      i + 1,
+				}, SessionID: sessionID})
+				return
+			}
 		}
 	}