feat: add research decks with WebMCP controls

src/features/decks/use-deck.ts

@@ -0,0 +1,39 @@
+import { useEffect, useState } from 'react'
+import { type Deck, deckSchema, EMPTY_DECK } from './model'
+
+export const DECK_STORAGE_KEY = 'twitter-lite-research-deck'
+
+export function useDeck() {
+  const [deck, setDeck] = useState<Deck>(EMPTY_DECK)
+  const [ready, setReady] = useState(false)
+  const [storageError, setStorageError] = useState<string>()
+
+  useEffect(() => {
+    try {
+      const saved = localStorage.getItem(DECK_STORAGE_KEY)
+      if (saved !== null) setDeck(deckSchema.parse(JSON.parse(saved)))
+    } catch {
+      setStorageError(
+        '保存したデッキを読み込めませんでした。編集内容を保存すると、このブラウザのデッキを置き換えます。',
+      )
+    }
+    setReady(true)
+  }, [])
+
+  function save(next: Deck) {
+    const validated = deckSchema.parse(next)
+    setDeck(validated)
+    try {
+      localStorage.setItem(DECK_STORAGE_KEY, JSON.stringify(validated))
+      setStorageError(undefined)
+      return true
+    } catch {
+      setStorageError(
+        'このブラウザに保存できません。現在の変更は、ページを閉じると失われます。',
+      )
+      return false
+    }
+  }
+
+  return { deck, ready, storageError, save }
+}