refactor: 拆分 cockpit 為可個別安裝的 statusbar 與 companion

- statusbar：輸入框上方狀態列，指令 /statusbar
- companion：小說角色陪伴，指令 /companion，自行渲染角色行
- companion 資料目錄改為 ~/.companion
- 整併 M4 檔案至 companion；M2 實作移至 hooks/companion/persona
- README 移除本機資料夾安裝，補上更新與移除指令

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

plugins/statusbar/.claude-plugin/plugin.json

@@ -0,0 +1,10 @@
+{
+  "name": "statusbar",
+  "version": "0.1.0",
+  "description": "輸入框上方的單行狀態列：模型、目錄、分支、5h/7d 額度與重置、context、CPU/記憶體/磁碟",
+  "license": "MIT",
+  "types": "./types/index.d.ts",
+  "author": {
+    "name": "JSC"
+  }
+}