Add FiveM Lua Extension

[manipou]

Summary

This pull request registers the fivem-lua extension in the Zed marketplace registry.

It provides comprehensive autocompletion, rich snippets, interactive parameter placeholders, and hover documentation for 5,300+ FiveM Lua native functions, core runtime utilities, and fxmanifest.lua templates.

• Submodule Path: extensions/fivem-lua
• Submodule Repo: https://github.com/manipou/fivem-lua-zed
• License: MIT (included at the root of the submodule repository)

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Key Features

• 5,300+ Native APIs: Includes the entire native registry directly from the official FiveM documentation.
• PascalCase Only: Focuses exclusively on standard PascalCase definitions (e.g. GetPlayerPed), keeping the autocomplete menu clean and distraction-free.
• Interactive Parameter Tab-Stops: Auto-populates parameters as interactive placeholders (${1:entity}, ${2:x}, etc.) so developers can press Tab to fill in arguments quickly.
• Overload Support: Correctly groups and supports client/server/shared native variations. Different parameter signatures appear as distinct autocomplete options in the editor and are declared as standard ---@overload annotations in the library stubs (preventing LSP warnings).
• FiveM Utility Helpers: Adds custom templates for event handlers (RegisterNetEvent, AddEventHandler), loop threads (CreateThread, Wait), NUI messaging (RegisterNUICallback, SendNUIMessage), and a comprehensive fxmanifest.lua boilerplate.

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Checklist

• Extension directory contains a valid, accepted open-source license.
• extensions.toml and .gitmodules entries are alphabetically sorted (validated with bun run sort-extensions / pnpm sort-extensions).
• Submodule is added using an HTTPS URL (https://github.com/manipou/fivem-lua-zed.git).
• Installed and thoroughly tested locally as a dev extension in Zed.