Add web search knowledge base, message tagging, and word-memory tip topics

Introduces websearch.py (Tavily) + knowledge.py to ground chat responses
in search results, tagging.py to tag user and assistant messages via LLM
and pick related topics for the Discord useless-tips job, and
word_memory.py to track recent conversation nouns (surfaced in the new
WordPool.vue sidebar) used to pick tip topics close to a related tag.

backend/app/core/memory.py

@@ -2,15 +2,21 @@ from sqlalchemy.orm import Session as DBSession
 from app.db.models import Memory, Message, Session
 from app.core.config import MEMORY_SUMMARIZE_THRESHOLD
 from app.core import llm
+from app.core import knowledge
+from app.core.tagging import tag_memory
 
 
 def get_context_messages(db: DBSession, session_id: str) -> list[dict]:
-    """短期メモリ（最近のメッセージ）と長期メモリ（要約）を結合してコンテキストを返す。"""
+    """蓄積知識・長期メモリ（要約）・短期メモリ（最近のメッセージ）を結合してコンテキストを返す。"""
     memories = db.query(Memory).filter(Memory.session_id == session_id).order_by(Memory.created_at).all()
     messages = db.query(Message).filter(Message.session_id == session_id).order_by(Message.created_at).all()
 
     context: list[dict] = []
 
+    knowledge_context = knowledge.get_knowledge_context(db)
+    if knowledge_context:
+        context.append({"role": "system", "content": knowledge_context})
+
     if memories:
         combined_summary = "\n\n".join(m.summary for m in memories)
         context.append({
@@ -36,9 +42,13 @@ async def maybe_summarize(db: DBSession, session: Session) -> None:
         {"role": "system", "content": "以下の会話を簡潔に要約してください。重要な事実・決定・文脈を保持してください。"},
         *[{"role": m.role, "content": m.content} for m in to_summarize],
     ]
-    summary_text = await llm.complete(summary_prompt, session_id=session.id)
+    summary_text = await llm.complete(summary_prompt, model=session.model, session_id=session.id)
 
-    db.add(Memory(session_id=session.id, summary=summary_text))
+    memory = Memory(session_id=session.id, summary=summary_text)
+    db.add(memory)
     for msg in to_summarize:
         db.delete(msg)
     db.commit()
+    db.refresh(memory)
+
+    await tag_memory(db, memory)