feat: VSCode and Neovim editor extensions

[daavidrgz]

Summary

Package the existing LSP (crates/lsp) into polished editor extensions for VSCode and Neovim.

Motivation

The hard part — the LSP implementation — already exists. But most users won't manually configure an LSP. Packaging it into discoverable extensions would:

1. Drive adoption — VSCode marketplace and Neovim plugin lists are discovery channels
2. Improve DX — Syntax highlighting, completions, and error diagnostics out of the box
3. Showcase gq's capabilities — The LSP is a unique differentiator vs. jq; it should be visible

Scope

VSCode Extension

• Language registration for .gq files and embedded queries
• Syntax highlighting (TextMate grammar)
• LSP client wiring to the gq LSP binary
• Marketplace publishing with README, icon, screenshots

Neovim Plugin

• nvim-lspconfig integration (register gq-lsp as a known server)
• Tree-sitter grammar for syntax highlighting
• Standalone plugin with setup instructions for lazy.nvim / packer

Considerations

• How should the LSP binary be distributed? Bundled with the extension, or require separate install?
• Should the extensions support inline gq queries in JSON/YAML files?
• The LSP completion escaping bug (keys with special characters) in crates/lsp/src/lib.rs should be fixed first