Add language server executable

[rentziass]

This adds an executable for the language server so that people not using the VSCode extension can easily start using it. I'm also adding a little documentation of how to run this in Neovim and locally.

Covers #56 and hopefully helps with #148.

[Copilot]

Pull request overview

This PR adds a standalone CLI executable for the Actions language server, enabling users who don't use VS Code to utilize the language server with their preferred editors. The changes include build configuration for bundling the executable, a bin entry point, and comprehensive documentation for setup in Neovim.

Key changes:

• Added esbuild-based CLI bundling to create a standalone executable
• Introduced a bin script (actions-languageserver) that can be installed globally via npm
• Added detailed documentation for using the language server in Neovim with LSP configuration examples

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 4 comments.

File	Description
languageserver/package.json	Added bin entry, esbuild dependency, and build scripts for CLI bundling
languageserver/bin/actions-languageserver	New executable entry point that loads the bundled language server
languageserver/README.md	Added comprehensive documentation for CLI usage, Neovim setup, and local development
package-lock.json	Updated with esbuild dependencies and platform-specific optional dependencies

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