refactor: jsc-mod 改名 jsc-mod-statusline、jsc-companion 改名 jsc-mod-companion,指令拆成獨立指令

- jsc-mod-statusline:/jsc-mod-statusline:enable、compact、disable
- jsc-mod-companion:/jsc-mod-companion:status、switch、disable、setup、todo、quiet
- 同步更新 plugin.json、marketplace.json 與各 README
- 補上 statusline band 測試缺少的 ui.render 底層處理

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

plugins/jsc-mod-companion/hooks/companion/io.ts

@@ -0,0 +1,33 @@
+// 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))