Add mq extension

[harehare]

Adds mq language support for mq, a jq-like command-line tool for Markdown processing.

• Registers the mq extension in extensions.toml
• Adds harehare/zed-mq as the extension submodule
• Downloads mq-lsp binary automatically from GitHub releases
• Includes Tree-sitter grammar, syntax highlighting, LSP support, and AI Assistant slash commands

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[harehare]

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We require contributors to sign our Contributor License Agreement, and we don't have @harehare on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

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[harehare]

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