SKILL.md: remove hardcoded local path, simplify install

Agent should use global `snowball` command, not local dev path.
Only show install hint if command is missing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baixianger

SKILL.md

@@ -27,9 +27,10 @@ snowball fund 110011 --growth        # 基金收益
 
 ## 安装
 
+如果 `snowball` 命令不存在，提示用户运行：
+
 ```bash
-npm install -g snowball-cli          # 或
-bun add -g snowball-cli
+npm install -g snowball-cli
 ```
 
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