Auto-detect and prefer user-installed CLI tools over built-in

### Describe the feature or problem you'd like to solve

The agent has no mechanism to discover equivalent tools on PATH to either opt for them first or use them as a fallback. It continues with a failing or inferior tool

### Proposed solution

- Reduces friction
- Reduces wasted turns
- It uses the tools that I use so I can easily trace what happened

### Example prompts or workflows

- "Find all usages of interface across this repo"
- "Lint all the modified typescript files"
- "Search this project for todo comments and summarize them"
- "Run tests for this module/component. Iterate until they pass"
- "Find all files larger than 1 mb in this directory and sub directories

### Additional context

_No response_

該 issue 未指出用於 PATH 探索和工具偏好的檔案、測試或進入點。首先定位 CLI 內建的工具定義和命令執行流程；完成的標準是，能夠探索等效的使用者安裝工具，並在列出的工作流程中優先使用它們或將其作為 fallback。

由索引模型根據 Issue 內容生成。