fix(knowledge): 草稿的过程段写「收件箱 → 待办」，而不是两句「状态变更」

自动生成的草稿里，时间线只查了 activity.action，没带 payload，
于是每条状态变化都变成一模一样的「状态变更」，读者看不出事情怎么走的。

- services/knowledge.snapshot_source 多取 Activity.payload 一起交给渲染
- domain/knowledge 加 STATUS_LABEL 与 _describe()，把 payload 的 from/to 翻成人话
- 新增用例断言草稿里有「待办 → 进行中」「进行中 → 已完成」

66 passed。

backend/app/domain/knowledge.py

@@ -53,6 +53,36 @@ ACTION_LABEL: dict[str, str] = {
     "knowledge_created": "沉淀为知识",
 }
 
+# 状态流转在时间线里要写成人话：「待办 → 进行中」，光写"状态变更"等于没写
+STATUS_LABEL: dict[str, str] = {
+    "inbox": "收件箱",
+    "todo": "待办",
+    "doing": "进行中",
+    "blocked": "被阻塞",
+    "done": "已完成",
+    "canceled": "已取消",
+    "open": "待接收",
+    "accepted": "已接受",
+    "in_progress": "办理中",
+    "pending_verify": "待验收",
+}
+
+
+def _describe(row: dict[str, Any]) -> str:
+    """一条活动怎么念给读者听。"""
+    action = str(row.get("action") or "")
+    label = ACTION_LABEL[action]
+    payload = row.get("payload") or {}
+    if action == "status_changed" and isinstance(payload, dict):
+        src, dst = payload.get("from"), payload.get("to")
+        if src and dst:
+            from_label = STATUS_LABEL.get(str(src), str(src))
+            to_label = STATUS_LABEL.get(str(dst), str(dst))
+            return f"{from_label} → {to_label}"
+    if action == "knowledge_created" and isinstance(payload, dict) and payload.get("doc_type"):
+        return f"{label}（{payload.get('doc_type')}）"
+    return label
+
 
 def target_status(action: str, current: str) -> str:
     """动作 → 目标状态。非法组合抛 7003，并把"现在还能做什么"带回去。"""
@@ -160,7 +190,7 @@ def render_draft(
         out.append("## 过程")
         out.append("")
         for r in rows:
-            out.append(f"- {_fmt(r.get('at'))} {ACTION_LABEL[r['action']]}")
+            out.append(f"- {_fmt(r.get('at'))} {_describe(r)}")
         out.append("")
 
     if resolution_md.strip():