fix: emit phase_start in sequential streaming path

Without phase_start, the frontend had no panel created until the first
agent_event arrived (30+ seconds after plan_done), making it look like
nothing was happening.

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

backend/app/services/team_orchestrator.py

@@ -929,6 +929,25 @@ class TeamOrchestrator:
         else:
             # ─── 顺序执行（流式：每 phase 实时推送 Agent 内部事件） ───
             for i, phase in enumerate(phases):
+                phase_num = phase.get("phase", i + 1)
+                role = phase.get("role", "developer")
+                phase_name = phase.get("name", f"阶段 {phase_num}")
+
+                agent = self._get_agent_by_role(members, role)
+                if not agent:
+                    yield {"type": "phase_done", "phase": phase_num, "name": phase_name,
+                           "role": role, "success": False, "error": f"missing_role:{role}"}
+                    all_outputs.append(f"[跳过] 阶段 {phase_num} ({phase_name}): 无 {role} 角色")
+                    continue
+
+                yield {
+                    "type": "phase_start",
+                    "phase": phase_num,
+                    "name": phase_name,
+                    "role": role,
+                    "agent": agent.name,
+                }
+
                 event_queue = asyncio.Queue()
                 task = asyncio.create_task(
                     self._run_phase_stream_and_collect(
@@ -947,19 +966,16 @@ class TeamOrchestrator:
                     r = task.result()
                 except Exception as exc:
                     r = {
-                        "phase": phase.get("phase", i + 1),
+                        "phase": phase_num,
-                        "name": phase.get("name", ""),
+                        "name": phase_name,
-                        "role": phase.get("role", ""),
+                        "role": role,
-                        "agent_name": None,
+                        "agent_name": agent.name,
                         "output": f"执行异常: {exc}",
                         "success": False, "error": str(exc),
                         "files": [],
                     }
 
                 output_text = r.get("output", "")
-                phase_num = r["phase"]
-                phase_name = r["name"]
-                role = r["role"]
 
                 if r.get("success"):
                     context_doc += f"\n## 阶段 {phase_num}: {phase_name}\n{output_text[:2000]}\n"