chore(deps): 将包管理器从 npm 迁移到 pnpm

- docs: 更新 README 和 README_CN 中的安装说明
- build: 添加 pnpm-lock.yaml 和 .npmrc 配置
- build: 删除 package-lock.json 锁文件
- fix: 解决 peer dependency 冲突（legacy-peer-deps）
- perf: pnpm 提供更快的安装速度和更小的磁盘占用

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

README.md

@@ -218,20 +218,23 @@ Build and run from source code for development or customization.
 git clone https://github.com/Wei-Shaw/sub2api.git
 cd sub2api
 
-# 2. Build frontend
+# 2. Install pnpm (if not already installed)
+npm install -g pnpm
+
+# 3. Build frontend
 cd frontend
-npm install
-npm run build
+pnpm install
+pnpm run build
 # Output will be in ../backend/internal/web/dist/
 
-# 3. Build backend with embedded frontend
+# 4. Build backend with embedded frontend
 cd ../backend
 go build -tags embed -o sub2api ./cmd/server
 
-# 4. Create configuration file
+# 5. Create configuration file
 cp ../deploy/config.example.yaml ./config.yaml
 
-# 5. Edit configuration
+# 6. Edit configuration
 nano config.yaml
 ```
 
@@ -291,7 +294,7 @@ go run ./cmd/server
 
 # Frontend (with hot reload)
 cd frontend
-npm run dev
+pnpm run dev
 ```
 
 #### Code Generation