fix: replace hardcoded ~/.desirecore paths with ${DESIRECORE_ROOT} variable (#16)

## Summary

- 将所有技能文件中的硬编码 `~/.desirecore/` 和 `$HOME/.desirecore/` 路径替换为
`${DESIRECORE_ROOT}/` 变量
- 递增 manifest.json version 至 1.2.1

## Why

dev 模式下 `DESIRECORE_HOME=~/.desirecore-dev`，硬编码路径导致技能读取错误的端口文件和目录。主仓库的
`variable-substitutor.ts` 会在运行时将 `${DESIRECORE_ROOT}` 替换为实际根目录。

## Test plan

- [ ] `npm run dev` 启动后触发任意技能，确认端口路径解析为
`~/.desirecore-dev/agent-service.port`
- [ ] prod 模式确认路径为 `~/.desirecore/agent-service.port`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

skills/nodejs-runtime/references/package-managers.md

@@ -12,7 +12,7 @@
 ## 通过 DesireCore Volta 安装
 
 ```bash
-VOLTA=~/.desirecore/runtime/volta/volta
+VOLTA=${DESIRECORE_ROOT}/runtime/volta/volta
 export VOLTA_FEATURE_PNPM=1
 
 "$VOLTA" install pnpm@latest
@@ -23,7 +23,7 @@ export VOLTA_FEATURE_PNPM=1
 或 HTTP API：
 
 ```bash
-BASE="https://127.0.0.1:$(cat ~/.desirecore/agent-service.port)/api/runtime"
+BASE="https://127.0.0.1:$(cat ${DESIRECORE_ROOT}/agent-service.port)/api/runtime"
 curl -sk -X POST "${BASE}/pkg/pnpm/install" -H "Content-Type: application/json" -d '{"version":"latest"}'
 ```