feat(agent): stream live agent output to issue detail page

When an agent is working on an issue, users can now see real-time output
in the issue detail page instead of waiting for completion.

Backend:
- Add task_message table and migration for persisting agent messages
- Add POST /api/daemon/tasks/{id}/messages endpoint for daemon to report
  structured messages (tool_use, tool_result, text, error) in batches
- Add GET /api/daemon/tasks/{id}/messages for catch-up after reconnect
- Add GET /api/issues/{id}/active-task to check for running tasks
- Broadcast task:message events via WebSocket
- Daemon forwards agent session messages with 500ms text throttling

Frontend:
- Add AgentLiveCard component showing live tool calls, text output,
  and progress indicators with auto-scroll
- Wire into issue detail timeline with WS subscription and HTTP catch-up
- Card appears when agent is working, disappears on completion/failure

server/pkg/db/generated/agent.sql.go

@@ -451,6 +451,48 @@ func (q *Queries) HasPendingTaskForIssue(ctx context.Context, issueID pgtype.UUI
 	return has_pending, err
 }
 
+const listActiveTasksByIssue = `-- name: ListActiveTasksByIssue :many
+SELECT id, agent_id, issue_id, status, priority, dispatched_at, started_at, completed_at, result, error, created_at, context, runtime_id, session_id, work_dir FROM agent_task_queue
+WHERE issue_id = $1 AND status IN ('dispatched', 'running')
+ORDER BY created_at DESC
+`
+
+func (q *Queries) ListActiveTasksByIssue(ctx context.Context, issueID pgtype.UUID) ([]AgentTaskQueue, error) {
+	rows, err := q.db.Query(ctx, listActiveTasksByIssue, issueID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []AgentTaskQueue{}
+	for rows.Next() {
+		var i AgentTaskQueue
+		if err := rows.Scan(
+			&i.ID,
+			&i.AgentID,
+			&i.IssueID,
+			&i.Status,
+			&i.Priority,
+			&i.DispatchedAt,
+			&i.StartedAt,
+			&i.CompletedAt,
+			&i.Result,
+			&i.Error,
+			&i.CreatedAt,
+			&i.Context,
+			&i.RuntimeID,
+			&i.SessionID,
+			&i.WorkDir,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listAgentTasks = `-- name: ListAgentTasks :many
 SELECT id, agent_id, issue_id, status, priority, dispatched_at, started_at, completed_at, result, error, created_at, context, runtime_id, session_id, work_dir FROM agent_task_queue
 WHERE agent_id = $1