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/io.ts

@@ -0,0 +1,53 @@
+// 檔案系統與時鐘由外部注入，核心不直接碰真實環境
+export interface Fs {
+  read(path: string): Promise<string | null>
+  /** 原子寫入：先寫暫存檔再改名 */
+  write(path: string, data: string): Promise<void>
+}
+
+export type Clock = () => number
+
+export function memoryFs(): Fs & { files: Map<string, string> } {
+  const files = new Map<string, string>()
+  return {
+    files,
+    async read(p) {
+      return files.get(p) ?? null
+    },
+    async write(p, d) {
+      files.set(p, d)
+    },
+  }
+}
+
+export async function readJson<T>(fs: Fs, path: string, fallback: T): Promise<T> {
+  const raw = await fs.read(path)
+  if (raw === null) return fallback
+  try {
+    return JSON.parse(raw) as T
+  } catch {
+    return fallback
+  }
+}
+
+export const writeJson = (fs: Fs, path: string, value: unknown) => fs.write(path, JSON.stringify(value, null, 2))
+
+export async function nodeFs(): Promise<Fs> {
+  const { readFile, writeFile, rename, mkdir } = await import('node:fs/promises')
+  const { dirname } = await import('node:path')
+  return {
+    async read(p) {
+      try {
+        return await readFile(p, 'utf8')
+      } catch {
+        return null
+      }
+    },
+    async write(p, d) {
+      await mkdir(dirname(p), { recursive: true })
+      const tmp = `${p}.${process.pid}.tmp`
+      await writeFile(tmp, d)
+      await rename(tmp, p)
+    },
+  }
+}