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/api/notes.py

@@ -3,12 +3,12 @@ import zipfile
 from datetime import datetime, timezone
 from urllib.parse import quote
 
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, File, HTTPException, UploadFile
 from fastapi.responses import Response
 from pydantic import BaseModel
 from sqlalchemy.orm import Session as DBSession
 
-from app.core.notes import next_position, reorder, rename_section, set_section
+from app.core.notes import import_files, next_position, reorder, rename_section, set_section
 from app.db.database import get_db
 from app.db.models import NotePage
 
@@ -129,6 +129,24 @@ def create_page(req: NotePageCreate, db: DBSession = Depends(get_db)):
     return page
 
 
+@router.post("/import", response_model=list[NotePageResponse], status_code=201)
+async def import_pages(files: list[UploadFile] = File(...), db: DBSession = Depends(get_db)):
+    """アップロードされたファイルをページとして取り込む。
+
+    .md / .txt はそのまま1ページ、.zip は中のテキストファイルを1つずつページにする
+    （ZIP内のフォルダ名がセクションになるので、エクスポートしたZIPをそのまま戻せる）。
+    対象外の拡張子や大きすぎるファイルは黙って飛ばすので、1つも取り込めなければ 400。
+    """
+    payload = [(f.filename or "無題", await f.read()) for f in files]
+    created = import_files(db, payload)
+    if not created:
+        raise HTTPException(
+            status_code=400,
+            detail="取り込めるファイルがありませんでした（.md / .txt / .zip のみ）",
+        )
+    return created
+
+
 @router.post("/sections/rename")
 def rename_section_endpoint(req: SectionRenameRequest, db: DBSession = Depends(get_db)):
     """old_name セクションに属する全ページを new_name セクションへ一括で付け替える。new_name が空ならグループ解除。"""