docs: 文档与站点链接随托管地迁移到 GitHub

go module 路径已迁到 `github.com/JianFeeeee/homeagentsdk`（见上一提交），
文档里的示例 import、Releases 下载地址、模块路径引用同步更新。

涉及：README.md、README_EN.md、docs/guide/{getting-started,first-plugin,
capability-boundary}.md、mkdocs.yml。

## 有意保留的 gitcode 提及

**不是漏改**，删了反而让文档说谎：

- README.md：「二进制的实际分发地址目前是 gitcode」——两个仓的 release
  附件不同步，只有二进制暂时还得去 gitcode 取
- mkdocs.yml：gitcode 镜像链接（国内直连更快，海外看 GitHub）
- docs/guide/getting-started.md：注明「gitcode 仅作国内镜像」

判据：**能照做的指引**优先于「链接好看」。读者照 README 下载 hmapdev
时，走 gitcode 是真能拿到东西的那条路。

README_EN.md

@@ -338,7 +338,7 @@ Plugin developers only need to implement the `Plugin` interface and export a `Ne
 `hmapdev` provides full development workflow support and produces `.hmap` plugin bundles (the tool is
 named after that package format). Prebuilt binaries ship as **release assets**
 (linux/darwin/windows × amd64/arm64); download from
-[Releases](https://gitcode.com/JianFeeeee/homeagent-sdk/releases) and put it on your PATH:
+[Releases](https://github.com/JianFeeeee/homeagentsdk/releases) and put it on your PATH:
 
 > Rename note: the toolchain was called `plugindev` and is `hmapdev` since 1.2.0.
 > The SDK store moved from `~/.homeagent/plugindev/sdk` to `~/.homeagent/hmapdev/sdk`
@@ -346,7 +346,7 @@ named after that package format). Prebuilt binaries ship as **release assets**
 
 ```bash
 # From release assets (latest SDK release / linux amd64 shown)
-curl -Lo hmapdev https://gitcode.com/JianFeeeee/homeagent-sdk/releases/download/<version>/hmapdev_linux_amd64
+curl -Lo hmapdev https://github.com/JianFeeeee/homeagentsdk/releases/download/<version>/hmapdev_linux_amd64
 chmod +x hmapdev
 
 # Or build from source