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/db/models.py

@@ -104,6 +104,22 @@ class LocalKnowledgeDoc(Base):
     updated_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
 
 
+class NotePage(Base):
+    """ユーザーとAIが共同で編集する共有ノートの1ページ。UIではタブとして表示する。
+
+    ページのタイトル一覧は毎回システムプロンプトに注入され、本文はモデルが
+    read_note ツールで読み出す（app.core.notes を参照）。
+    """
+    __tablename__ = "note_pages"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    title: Mapped[str] = mapped_column(String)
+    content: Mapped[str] = mapped_column(Text, default="")
+    position: Mapped[int] = mapped_column(Integer, default=0)  # タブの並び順
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+
+
 class AppSetting(Base):
     """GUIの設定画面から編集する接続情報（APIキー等）。app.core.settings_store が読み書きする。"""
     __tablename__ = "app_settings"