bug: Multiple issues with Amazon Q CLI: fs_write errors and inefficient file search operations

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue

### Operating system

Linux (Ubuntu/Debian-based distribution)

### Expected behaviour

Describe the bug
I'm encountering two issues when using Amazon Q CLI:

Frequent errors when trying to use the fs_write tool:
Amazon Q is having trouble responding right now:
0: failed to print tool, fs_write: No such file or directory (os error 2)
Location:
crates/chat-cli/src/cli/chat/mod.rs:1012

Inefficient file search: Amazon Q uses file enumeration instead of system search commands, which significantly slows down
operations.
Regression Issue

Select this option if this issue appears to be a regression.
Expected Behavior
The fs_write tool should work reliably without "No such file or directory" errors
When searching for files, Amazon Q should use system commands (find, grep, locate, etc.) for fast searching rather than
sequential file enumeration.

### Actual behaviour

Current Behavior
When trying to modify files, fs_write errors frequently occur, forcing me to use a workaround: creating a new file and renaming
it instead of direct editing.

When searching for files, Amazon Q "thinks" for a long time, going through files one by one instead of using system search
commands. When explicitly asked to use OS commands for searching, it starts using them and finds the necessary files almost
instantly.

### Steps to reproduce

Reproduction Steps
For fs_write error:
• Ask Amazon Q to modify the contents of an existing file
• Observe the "No such file or directory" error
• Suggest a workaround (create a new file and rename it)

For search issue:
• Ask to find a file in the system without specifying to use OS commands
• Observe long waiting time
• Ask to use find/grep/locate
• Observe instant results

Possible Solution
Fix path handling in the fs_write tool for correct operation with the file system
Optimize file search algorithms, using system search commands (find, grep, locate) by default instead of sequential enumeration
Additional Information/Context
These issues significantly reduce the efficiency of working with Amazon Q CLI. Workarounds exist, but they shouldn't be necessary
for basic functionality.

CLI version used
Amazon Q CLI (latest version)

首先重现 fs_write 失败，并检查 crates/chat-cli/src/cli/chat/mod.rs 中 1012 行附近的代码。然后跟踪在未请求 OS 搜索命令时使用的文件搜索路径。完成的标准是，编辑现有文件不再产生报告中的错误，并且文件搜索避免报告中的缓慢顺序行为；在 Ubuntu/Debian 上验证这两个重现案例。

由索引模型根据 Issue 内容生成。