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/minimax-image-gen/SKILL.md

@@ -44,7 +44,7 @@ metadata:
         Use this skill when the user wants to generate images using MiniMax's image-01 model. Supports text-to-image and subject reference for character consistency. Use when the user mentions generate images, draw a picture, text-to-image, create an image, AI painting, generate illustration, draw one for me, help me draw, design an image, MiniMax drawing.
       body: ./SKILL.md
       source_hash: sha256:4630268ef3bd4e23
-      translated_by: ai:claude-opus-4-7
+      translated_by: human
       translated_at: '2026-05-03'
 market:
   icon: >-
@@ -78,7 +78,7 @@ market:
 ### Step 1: Call the API to generate the image
 
 ```bash
-PORT=$(cat ~/.desirecore/agent-service.port)
+PORT=$(cat ${DESIRECORE_ROOT}/agent-service.port)
 curl -sk -X POST "https://127.0.0.1:${PORT}/api/media-proxy" \
   -H "Content-Type: application/json" \
   -d '{
@@ -100,7 +100,7 @@ Extract `data.data.image_urls[0]` from the JSON response to obtain the image URL
 ### Step 2: Download and upload to media-store
 
 ```bash
-PORT=$(cat ~/.desirecore/agent-service.port)
+PORT=$(cat ${DESIRECORE_ROOT}/agent-service.port)
 IMAGE_URL="第一步拿到的图片URL"
 curl -sL "$IMAGE_URL" -o /tmp/minimax-gen.png && \
 curl -sk -X POST "https://127.0.0.1:${PORT}/api/media/upload" \