refactor(rename)!: llmsproxy → modelrouter（module / 二进制 / 路径 / env）

产品名早已是 ModelRouter，但仓库标识符仍沿用旧名。这次统一，读写两侧都做兼容，
已部署的机器不会因为顺序问题立刻失效。

- go module `llmsproxy` → `modelrouter`；全仓 import 与 `cmd/modelrouter` 同步。
- `Makefile BINARY=modelrouter`；发行包名、systemd unit、/usr/share 资源、
  `/usr/local/bin` 目标全部改为 modelrouter。
- 默认配置目录 `/etc/llmsproxy` → `/etc/modelrouter`。**读取侧回退**：插件与
  `storeDir` 仍会检查旧路径，所以"先换二进制、后改 unit"不会立即失效。
- 环境变量 `LLMSPROXY_*`（PLUGIN_DIR / XDISPLAY_BASE / ARCH / LIVE_ZEN /
  BUILD_DIR）改为 `MODELROUTER_*`；`LLMS_PROXY_MASTER_KEY` →
  `MODELROUTER_MASTER_KEY`。旧名在读取侧继续接受。
- 桌面端内嵌核心 `bin/llmsproxy` → `bin/modelrouter`，并保留旧文件名回退，
  避免升级到一半的 profile 被判成"core binary missing"。
- 新增 `packaging/migrate-to-modelrouter.sh`：**默认 dry-run**，复制而非移动、
  旧目录永不删除、支持 `--rollback`；随 release tar 分发并由 core-dist 校验。
- `deploy.sh` 增加改名保护：发现旧 `/etc/llmsproxy` 而新配置不存在时**中止**，
  否则会部署出一个"能启动但没有 key、没有源"的空实例。
- 临时目录前缀 `/tmp/llmsproxy-*` → `/tmp/modelrouter-*`；清理逻辑同时回收两代。

兼容别名（`__llmsproxy_*` 全局、`llmsproxy` SDK 别名、旧路径/旧 env）刻意保留，
它们是升级路径而非遗留；docs/plugins.md 已标注为废弃。

本提交未包含：`adapters/opencodezen.lua`、`adapter_opencodezen_test.go`、
`adapter_opencodezen_live_test.go`（OpenCode UA/免费池的既有改动，另批提交）。

cmd/gui/scripts/prepare-core.js

@@ -1,5 +1,5 @@
 #!/usr/bin/env node
-// Build the embedded llmsproxy core(s) for the GUI package.
+// Build the embedded modelrouter core(s) for the GUI package.
 //   node prepare-core.js        -> linux (native, luajit) + win (cross, best effort)
 //   node prepare-core.js linux  -> linux only
 //   node prepare-core.js win    -> win only
@@ -12,21 +12,21 @@ const binDir = path.join(guiDir, "bin");
 const projectRoot = path.join(guiDir, "..", "..");
 
 function buildLinux() {
-  const out = path.join(binDir, "llmsproxy");
-  console.log("[prepare-core] building llmsproxy (linux/luajit)...");
+  const out = path.join(binDir, "modelrouter");
+  console.log("[prepare-core] building modelrouter (linux/luajit)...");
   fs.mkdirSync(binDir, { recursive: true });
   execFileSync(
     "go",
-    ["build", "-tags", "luajit", "-trimpath", "-o", out, "./cmd/llmsproxy"],
+    ["build", "-tags", "luajit", "-trimpath", "-o", out, "./cmd/modelrouter"],
     { cwd: projectRoot, stdio: "inherit" },
   );
   return out;
 }
 
 function buildWin() {
-  const out = path.join(binDir, "llmsproxy.exe");
+  const out = path.join(binDir, "modelrouter.exe");
   console.log(
-    "[prepare-core] cross-building llmsproxy.exe (windows/amd64, luajit)...",
+    "[prepare-core] cross-building modelrouter.exe (windows/amd64, luajit)...",
   );
   fs.mkdirSync(binDir, { recursive: true });
   const cc = process.env.MINGW_CC || "x86_64-w64-mingw32-gcc";
@@ -43,7 +43,7 @@ function buildWin() {
   }
   execFileSync(
     "go",
-    ["build", "-tags", "luajit", "-trimpath", "-o", out, "./cmd/llmsproxy"],
+    ["build", "-tags", "luajit", "-trimpath", "-o", out, "./cmd/modelrouter"],
     {
       cwd: projectRoot,
       stdio: "inherit",