feat(model): Top5#1 结构化流事件 + WS 事件体系（对齐 OpenClaw AssistantMessageEvent）

- 新增 model/stream.go：StreamKind(text/thinking/tool_call 各 start/delta/end + tool_execution)
  + StreamEvent{Kind,Delta,Index,ID}。
- ChatStream 签名 onChunk func(delta string)→onEvent func(StreamEvent)；loop OnStream 同改；
  streamStep 转发结构化事件。
- openai：text_delta + text_start/text_end（正文三段式）；anthropic：文本块 text_*/tool_call_*
  按块 Index（content_block_stop 分支）真分段；fallback：有事件即交付。
- ws_hub：wsEvent 壳补 turnId/seq；新增 broadcastStream；streamChat 每帧打 turnId+seq；
  stream.go 把事件 publish 到 bus ws.stream。
- ws_bridge：streamEventData 映射 text_*→message.start/delta/end、thinking_*→thinking.*、
  tool_call_*→tool_call.*、tool_execution_update→tool_execution.update，未知回退 stream_chunk。
- 前端 ws.ts：解析 message.start/delta/end、thinking.start/delta/end(pendingThinking)、
  tool_call.start/end→addTool、tool_execution.update；保留旧 stream_chunk/thinking/tool_used 兼容；
  types.ts 补 turnId/seq。Docs/api-client.md 增 §3.1 v0.4。

已知限制（注释/文档标注）：turnId 在 OnStream→bus→relay 路径暂为空（StreamEvent 无 turnId 字段，
bus ws.stream 载荷不带 turn）；OpenAI adapter 未解析 tool_call 段；thinking 段两 adapter 暂不发；
tool_execution.update 是保留项（随工具循环钩子后置）。go build/vet/test + 前端 tsc 全绿。

internal/services/gateway/extra_test.go

@@ -803,6 +803,40 @@ func TestHubStreamChat(t *testing.T) {
 	}
 }
 
+func TestHubBroadcastStream(t *testing.T) {
+	t.Parallel()
+	hb := newTestHub(nil, nil)
+	c := newFakeConn(hb, 32)
+	hb.register(c)
+
+	// A text_delta StreamEvent on the OnStream→bus→relay path becomes a typed
+	// message.delta frame carrying the delta text and a monotonically increasing
+	// seq, leaving the legacy stream_chunk shape out of the way.
+	hb.broadcastStream(model.StreamEvent{Kind: model.StreamKindTextDelta, Delta: "Hel", Index: 0})
+	ev := readFakeFrame(t, c)
+	if ev.Type != "message.delta" {
+		t.Fatalf("frame type = %q, want message.delta (frame=%+v)", ev.Type, ev)
+	}
+	data, ok := ev.Data.(map[string]any)
+	if !ok || data["delta"] != "Hel" {
+		t.Fatalf("frame data = %+v, want delta=Hel", ev.Data)
+	}
+	if ev.Seq != 1 {
+		t.Fatalf("frame seq = %d, want 1", ev.Seq)
+	}
+
+	// A tool_call event maps to tool_call.*; a non-StreamEvent payload is dropped.
+	hb.broadcastStream(model.StreamEvent{Kind: model.StreamKindToolCallEnd, ID: "toolu_1", Index: 0})
+	ev = readFakeFrame(t, c)
+	if ev.Type != "tool_call.end" {
+		t.Fatalf("second frame type = %q, want tool_call.end", ev.Type)
+	}
+	hb.broadcastStream("not-a-stream-event")
+	if err := connHasNoFrame(c); err != nil {
+		t.Fatalf("unexpected frame from non-StreamEvent payload: %v", err)
+	}
+}
+
 func TestHubStreamChatIdle(t *testing.T) {
 	t.Parallel()
 	hb := newTestHub(nil, nil) // nil runner