feat: Support bash command execution for Pochi workflows

[wsxiaoys]

Please describe the feature you want

Currently, Pochi workflows are limited to a predefined set of tools. This feature request proposes to add support for executing arbitrary bash commands within a Pochi workflow. This would significantly extend the power and flexibility of workflows, allowing them to interact with the shell and integrate with a much wider range of command-line tools and scripts.

This is inspired by the bash command execution in Claude Code: https://docs.claude.com/en/docs/claude-code/slash-commands#bash-command-execution

Additional context

Some relevant files in the codebase:

• packages/cli/src/lib/workflow-loader.ts
• packages/vscode/src/lib/env.ts
• packages/docs/content/docs/workflows.mdx

How it works in Claude Code

Execute bash commands before the slash command runs using the ! prefix. The output is included in the command context. You must include allowed-tools with the Bash tool, but you can choose the specific bash commands to allow.For example:

---
allowed-tools: Bash(git add:*), Bash(git status:*), Bash(git commit:*)
description: Create a git commit
---

## Context

- Current git status: !`git status`
- Current git diff (staged and unstaged changes): !`git diff HEAD`
- Current branch: !`git branch --show-current`
- Recent commits: !`git log --oneline -10`

## Your task

Based on the above changes, create a single git commit.

🤖 Generated with Pochi

[wsxiaoys]

i recommend we just run all these commands when sending the command, and attached them in a system-reminder section as part of the message