feat: M4 主動關心、待辦與記憶鞏固核心模組

- care：事件式關心（冷卻、每日上限、靜音、回覆中／輸入中不彈出），toast 與注入兩種輸出，台詞依觸發 × 個性 × 好感階段
- todo：新增、完成、承諾事項與到期提醒
- memory：檢索評分、遺忘曲線、鞏固與反思、金鑰過濾
- 以假時鐘與記憶體檔案系統測試核心接縫

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

plugins/hud/hooks/companion/todo.ts

@@ -0,0 +1,72 @@
+import type { Clock, Fs } from './io'
+import { readJson, writeJson } from './io'
+
+export interface Todo {
+  id: number
+  title: string
+  done: boolean
+  /** 承諾事項：助理答應記住的事 */
+  promise: boolean
+  dueAt?: number
+  createdAt: number
+  doneAt?: number
+  /** 已提醒過，避免重複 */
+  reminded?: boolean
+}
+
+export interface TodoList {
+  add(title: string, opts?: { promise?: boolean; dueAt?: number }): Promise<Todo>
+  complete(id: number): Promise<Todo | null>
+  list(opts?: { all?: boolean }): Promise<Todo[]>
+  /** 角色行顯示的待辦數（未完成） */
+  open(): Promise<number>
+  /** 取出到期且尚未提醒的項目，並標記為已提醒 */
+  due(): Promise<Todo[]>
+}
+
+export function createTodos(fs: Fs, clock: Clock, path: string): TodoList {
+  const load = () => readJson<Todo[]>(fs, path, [])
+  const save = (t: Todo[]) => writeJson(fs, path, t)
+  return {
+    async add(title, opts = {}) {
+      const all = await load()
+      const t: Todo = {
+        id: all.reduce((m, x) => Math.max(m, x.id), 0) + 1,
+        title: title.trim(),
+        done: false,
+        promise: !!opts.promise,
+        dueAt: opts.dueAt,
+        createdAt: clock(),
+      }
+      all.push(t)
+      await save(all)
+      return t
+    },
+    async complete(id) {
+      const all = await load()
+      const t = all.find(x => x.id === id)
+      if (!t || t.done) return t ?? null
+      t.done = true
+      t.doneAt = clock()
+      await save(all)
+      return t
+    },
+    async list(opts = {}) {
+      const all = await load()
+      return opts.all ? all : all.filter(t => !t.done)
+    },
+    async open() {
+      return (await load()).filter(t => !t.done).length
+    },
+    async due() {
+      const all = await load()
+      const now = clock()
+      const hit = all.filter(t => !t.done && !t.reminded && t.dueAt !== undefined && t.dueAt <= now)
+      if (hit.length) {
+        for (const t of hit) t.reminded = true
+        await save(all)
+      }
+      return hit
+    },
+  }
+}