Add shared notes with tabbed pages editable by user and AI

Adds a note_pages table backing a tabbed notes panel where the user and
the model can both read and write. Only page titles (plus a short
preview) are injected into the system prompt on every turn; full page
content is kept out of context and fetched on demand via a read_note
tool, with write_note letting the model append to, replace, or create a
page.

Generalizes llm.resolve_web_search into resolve_tool_calls so the
tool-calling loop handles web_search and the new note tools through one
path. The chat stream emits a notes_updated SSE event when the model
edits a note so the frontend panel can refresh; local edits are tracked
as dirty and never clobbered by that refresh.

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

backend/app/core/memory_kb/memory.py

@@ -5,6 +5,7 @@ from app.core import llm
 from app.core.memory_kb import knowledge
 from app.core.memory_kb import local_knowledge
 from app.core.memory_kb.tagging import tag_memory
+from app.core import notes
 
 
 async def get_context_messages(db: DBSession, session_id: str) -> list[dict]:
@@ -18,6 +19,11 @@ async def get_context_messages(db: DBSession, session_id: str) -> list[dict]:
     if knowledge_context:
         context.append({"role": "system", "content": knowledge_context})
 
+    # 共有ノートは「タイトル一覧」だけを常時見せ、本文は read_note ツールで読ませる
+    notes_context = notes.get_notes_context(db)
+    if notes_context:
+        context.append({"role": "system", "content": notes_context})
+
     if messages:
         latest_user_message = next((m.content for m in reversed(messages) if m.role == "user"), "")
         local_kb_context = await local_knowledge.get_local_kb_context(db, latest_user_message)