bug: (short issue descriptionDuplicate ~/.local/bin in PATH due to incorrect path existence check in Amazon Q shell scripts)

### 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
Amazon Q shell scripts (profile.pre.bash and profile.post.bash) incorrectly check for the existence of ~/.local/bin in the PATH
variable, which leads to this path being added twice to the PATH. The current check [[ ":$PATH:" != ":$_Q_LOCAL_BIN:" ]] doesn't
properly detect if the path is already present.

Regression Issue

Select this option if this issue appears to be a regression.
Expected Behavior
The PATH variable should contain ~/.local/bin only once. The check in Amazon Q shell scripts should correctly detect if the path is
already present in PATH and not add it again.

### Actual behaviour

Current Behavior
The PATH variable contains ~/.local/bin twice:
/home/user/.local/bin:/other/paths:/home/user/.local/bin

This happens because:

~/.profile adds ~/.local/bin to PATH
Amazon Q shell scripts (profile.pre.bash and profile.post.bash) add it again due to incorrect path existence check

### Steps to reproduce

Reproduction Steps
Have ~/.local/bin added to PATH in ~/.profile (standard in many Linux distributions)
Install Amazon Q CLI
Check PATH variable with echo $PATH
Observe that ~/.local/bin appears twice in the PATH
Possible Solution
Replace the current check in both profile.pre.bash and profile.post.bash:

From:
bash
[[ ":$PATH:" != ":$_Q_LOCAL_BIN:" ]] && PATH="${PATH:+"$PATH:"}$_Q_LOCAL_BIN"

To a more accurate check using regex:
bash
if [[ ! "$PATH" =~ (^|:)"$_Q_LOCAL_BIN"(:|$) ]]; then
PATH="${PATH:+"$PATH:"}$_Q_LOCAL_BIN"
fi

This regex properly checks if the path exists as a complete segment in the PATH variable.

Additional Information/Context
This issue doesn't cause functional problems but is a minor inefficiency as the shell has to search the same directory twice when
looking for executables.

CLI version used
Amazon Q CLI (latest version)

まず profile.pre.bash と profile.post.bash を読み、次に ~/.local/bin がすでに PATH に存在する状態で問題を再現し、既存の存在チェックを調べます。各スクリプトが ~/.local/bin を単一の完全な PATH セグメントとして残すようになれば、Ubuntu/Debian の記載されたセットアップも含めて作業は完了です。

索引モデルが issue の本文から書いたものです。