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>

frontend/src/stores/chat.ts

@@ -18,6 +18,7 @@ export interface Message {
 export interface Toast {
   id: number
   message: string
+  kind: 'error' | 'success'
 }
 
 let toastSeq = 0
@@ -34,9 +35,9 @@ export const useChatStore = defineStore('chat', () => {
     sessions.value.find((s) => s.id === currentSessionId.value) ?? null,
   )
 
-  function pushToast(message: string, durationMs = 5000) {
+  function pushToast(message: string, kind: Toast['kind'] = 'error', durationMs = 5000) {
     const id = ++toastSeq
-    toasts.value.push({ id, message })
+    toasts.value.push({ id, message, kind })
     setTimeout(() => {
       toasts.value = toasts.value.filter((t) => t.id !== id)
     }, durationMs)
@@ -53,6 +54,8 @@ export const useChatStore = defineStore('chat', () => {
   async function selectSession(sessionId: string | null) {
     currentSessionId.value = sessionId
     messages.value = []
+    // プロンプトに載せるノートはセッションごとの設定なので、切り替えのたびに読み直す
+    useNotesStore().loadAttached(sessionId).catch(() => {})
     if (!sessionId) return
     try {
       const records = await fetchMessages(sessionId)
@@ -98,7 +101,7 @@ export const useChatStore = defineStore('chat', () => {
       const session = await importSession(payload)
       await loadSessions()
       await selectSession(session.id)
-      pushToast(`「${session.title}」をインポートしました`)
+      pushToast(`「${session.title}」をインポートしました`, 'success')
     } catch (e) {
       pushToast(`インポート失敗: ${e instanceof Error ? e.message : e}`)
     }
@@ -132,13 +135,18 @@ export const useChatStore = defineStore('chat', () => {
     const msgIdx = messages.value.length - 1  // reactive proxy 経由で更新するためインデックスを保持
     isStreaming.value = true
 
+    const notesStore = useNotesStore()
     streamChat(
       text,
       currentSessionId.value,
       selectedModel.value,
+      [...notesStore.attachedIds],
       (chunk) => {
         if (chunk.type === 'session_id' && chunk.value) {
           currentSessionId.value = chunk.value as string
+          // 新規セッションはこの時点で作られる。送信時に渡したノートの紐付けが
+          // サーバー側に保存されているので、その保存先を控え直す
+          notesStore.loadAttached(chunk.value as string).catch(() => {})
           loadSessions().catch((e) => pushToast(`セッション更新失敗: ${e.message}`))
         } else if (chunk.type === 'chunk' && chunk.value) {
           messages.value[msgIdx].content += chunk.value as string