fix(chat): Change the UI on output console and add spinner for writing process from agentic

[Randall-Jiang]

Problem

1. On previous output console, the UI shows bash, now it need to be shell
2. For writing the file, there is no spinner so it has perceived latency illusion.
   
3. For build failed case, the build log won't show up in code block and not formatted

Solution

1. Updated the console UI text to "shell".
2. Identified the issue where the toolUseEvent wasn't stopping during file writing, preventing the spinner from appearing in the chat. Resolved by adding an if statement to handle the toolUseInput case appropriately.
3. Formatted the output for stderr.

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[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
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[justinmk3]

Thanks for thinking about shared utils, but this is specific to CW client, so it should live in packages/core/src/shared/clients/codewhispererChatClient.ts.