chore(gui): 版本号 3.0.0（与内核同版本）

改名为 breaking：go module 路径、二进制名、`/etc` 配置目录、`LLMSPROXY_*`
环境变量全部变更，已部署实例必须跑 `packaging/migrate-to-modelrouter.sh`。
因此内核与桌面端一起升到 3.0.0，而不是继续在 v2.0.x 上打 patch。

`Makefile` 的 VERSION 来自 `git describe`，无需另改。

cmd/gui/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "modelrouter-gui",
-  "version": "2.0.49",
+  "version": "3.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "modelrouter-gui",
-      "version": "2.0.49",
+      "version": "3.0.0",
       "license": "Proprietary",
       "devDependencies": {
         "electron": "^33.0.0",

cmd/gui/package.json

@@ -1,6 +1,6 @@
 {
   "name": "modelrouter-gui",
-  "version": "2.0.49",
+  "version": "3.0.0",
   "description": "ModelRouter Desktop — embedded ModelRouter core with tray",
   "author": "ModelRouter",
   "main": "main.js",