Show tool and web search activity in the chat UI

Tool calls were invisible until the answer arrived: the only trace was the
sources list, and only for web searches. Surface them as they happen instead.

Add llm.stream_tool_calls(), an incremental version of resolve_tool_calls()
that yields a start and a completion event per tool call and ends with a
"resolved" event carrying the previous return value. resolve_tool_calls() is
kept as a thin wrapper that drops the progress events.

api/chat.py relays those events as a new SSE "tool" event, and wraps the
search-summary/knowledge-save step in one of the same shape, since it is a
noticeable pause of its own.

On the front end, ToolActivityList.vue renders one row per tool above the
assistant bubble (label, target, spinner while running, short result when
done). The store merges events by id and marks anything still running as
interrupted when the stream ends early. Display only - not persisted, so the
rows disappear when the session is reloaded, same as sources.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/app/api/chat.py

@@ -216,9 +216,18 @@ async def stream_chat(req: ChatRequest, db: DBSession = Depends(get_db)):
         used_model = req.model or session.model
         full_response = []
         try:
-            resolved_context, searches, notes_changed = await llm.resolve_tool_calls(
+            # ツールの実行状況は tool イベントとしてそのままフロントへ流し、GUIに進行状況を出す
+            resolved_context, searches, notes_changed = context, [], False
+            async for event in llm.stream_tool_calls(
                 context, model=used_model, session_id=session.id, db=db,
-            )
+            ):
+                if event["type"] == "resolved":
+                    resolved_context = event["messages"]
+                    searches = event["searches"]
+                    notes_changed = event["notes_changed"]
+                else:
+                    yield sse({"type": "tool", "value": {k: v for k, v in event.items() if k != "type"}})
+
             if notes_changed:
                 # AIがノートを書き換えたので、フロントのノートパネルを再読み込みさせる
                 yield sse({"type": "notes_updated"})
@@ -228,11 +237,25 @@ async def stream_chat(req: ChatRequest, db: DBSession = Depends(get_db)):
                     for s in searches for r in s["results"]
                 ]
                 yield sse({"type": "sources", "value": sources})
+                yield sse({"type": "tool", "value": {
+                    "id": "save_knowledge",
+                    "name": "save_knowledge",
+                    "label": "検索結果を要約して保存",
+                    "detail": " / ".join(s["query"] for s in searches),
+                    "status": "running",
+                }})
+                saved = 0
                 for s in searches:
                     headline, summary = await knowledge.summarize_results(s["query"], s["results"])
                     if summary:
                         knowledge.save_knowledge(db, s["query"], summary, s["results"], headline=headline)
                         local_knowledge.save_search_result(s["query"], summary, s["results"])
+                        saved += 1
+                yield sse({"type": "tool", "value": {
+                    "id": "save_knowledge",
+                    "status": "done",
+                    "result": f"{saved}件を蓄積知識に保存" if saved else "保存できる要約なし",
+                }})
 
             # 履歴にtool_callsが含まれる場合、最終呼び出しにも同じツール定義を渡す必要がある
             used_tools = [WEB_SEARCH_TOOL, *NOTE_TOOLS] if len(resolved_context) > len(context) else None