Pin notes to a chat, and import notes from files

Two additions to the shared notes, both about getting content in and out of
the prompt.

Per-chat pinning. Notes normally reach the model as a title list only, and
the body arrives just if the model decides to call read_note. A 📌 on the tab
now puts a page's full body in the system prompt for the chat that is open,
every turn, no tool round trip. The selection is per session (new table
session_note_pages, unique on session_id + page_id), so different
conversations carry different pages. The title list marks pinned pages so the
model does not read them twice, and bodies are capped per page by
SESSION_NOTES_CONTENT_LIMIT.

A new chat has no session row until its first message, so the front end
cannot PUT the selection yet. POST /chat/stream therefore accepts
note_page_ids and applies it before building the context, which makes the
pins count from the very first turn.

File import. Dropping .md/.txt on the editor - or picking them with the new
⬆ button - creates pages, and a .zip is unpacked into one page per text
entry with the first path component as the section. That is exactly the
shape the export writes, so a downloaded zip round-trips back in. Titles that
collide get a " (2)" suffix rather than overwriting, since restoring a backup
into a live workspace should not destroy anything. UploadFile needs
python-multipart, added to the lockfile.

Toasts grew a kind: the import success message was rendering in the red error
toast, as was the existing session-import message. Both are green now.

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

backend/app/db/models.py

@@ -1,5 +1,5 @@
 from datetime import datetime, timezone
-from sqlalchemy import String, Text, ForeignKey, Integer, Float
+from sqlalchemy import String, Text, ForeignKey, Integer, Float, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from app.db.database import Base
 from app.db.types import UtcDateTime
@@ -16,6 +16,7 @@ class Session(Base):
 
     messages: Mapped[list["Message"]] = relationship(back_populates="session", cascade="all, delete-orphan", order_by="Message.created_at")
     memories: Mapped[list["Memory"]] = relationship(back_populates="session", cascade="all, delete-orphan")
+    note_links: Mapped[list["SessionNotePage"]] = relationship(back_populates="session", cascade="all, delete-orphan")
 
 
 class Message(Base):
@@ -119,7 +120,8 @@ 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）。
+    read_note ツールで読み出す（app.core.notes を参照）。ただし SessionNotePage で
+    セッションに紐付けられたページは、本文もそのままシステムプロンプトに載る。
     """
     __tablename__ = "note_pages"
 
@@ -131,6 +133,28 @@ class NotePage(Base):
     created_at: Mapped[datetime] = mapped_column(UtcDateTime, default=lambda: datetime.now(timezone.utc))
     updated_at: Mapped[datetime] = mapped_column(UtcDateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
 
+    session_links: Mapped[list["SessionNotePage"]] = relationship(back_populates="page", cascade="all, delete-orphan")
+
+
+class SessionNotePage(Base):
+    """「このセッションではこのページの本文をプロンプトに載せる」という指定。
+
+    通常、共有ノートはタイトル一覧だけがシステムプロンプトに入り、本文はモデルが
+    read_note ツールで取りに行く。ここに登録されたページはそれを待たず、本文が毎回
+    そのままシステムプロンプトに入る（app.core.notes.get_session_notes_context を参照）。
+    セッション単位なので、会話ごとに違う組み合わせを選べる。
+    """
+    __tablename__ = "session_note_pages"
+    __table_args__ = (UniqueConstraint("session_id", "page_id", name="uq_session_note_page"),)
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    session_id: Mapped[str] = mapped_column(ForeignKey("sessions.id", ondelete="CASCADE"))
+    page_id: Mapped[int] = mapped_column(ForeignKey("note_pages.id", ondelete="CASCADE"))
+    created_at: Mapped[datetime] = mapped_column(UtcDateTime, default=lambda: datetime.now(timezone.utc))
+
+    session: Mapped["Session"] = relationship(back_populates="note_links")
+    page: Mapped["NotePage"] = relationship(back_populates="session_links")
+
 
 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。"""