Add Clawdbot comparison section to README

[Copilot]

Issue asks how Crabcode differs from Clawdbot. The projects serve entirely different purposes but the distinction wasn't documented.

Changes

• Added comparison section to README clarifying that Crabcode is a tmux-based workspace manager for multi-repo development, while Clawdbot is a personal AI assistant with messaging integrations
• Positioned section prominently after the project tagline for immediate visibility
• Structured as side-by-side comparison covering: purpose, use cases, key features, tech stack, and target audience

The two projects have zero functional overlap.

Original prompt

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This section details on the original issue you should resolve

<issue_title>How is this different than https://github.com/clawdbot/clawdbot</issue_title>
<issue_description>?</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes How is this different than https://github.com/clawdbot/clawdbot #9

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