Clarify third-party status: not an xAI official plugin

Remove “official plugin format” wording; state community ownership
and local plugin install only in README, package, skill, and install copy.

package.json

@@ -1,7 +1,7 @@
 {
   "name": "grok-build-hud",
   "version": "0.3.12",
-  "description": "Grok Build 插件：同窗口实时状态条（上下文、配额、token、工具与待办）；plugin + CLI + tmux HUD",
+  "description": "第三方 Grok Build 状态条（非 xAI 官方）：同窗口上下文/配额/token/工具；plugin + CLI + tmux HUD",
   "type": "module",
   "main": "dist/src/index.js",
   "bin": {