Move language server command to explicit lsp subcommand

[purefunctor]

Goal

Require the explicit alexandrite lsp subcommand to start the language server, rather than starting it implicitly when no subcommand is supplied. Keep language-server options under lsp rather than accepting them at the top level.

The CLI already exposes an lsp subcommand, but currently also flattens its options into the top-level CLI and defaults to launching the language server.

This is a breaking change for clients that launch Alexandrite without the subcommand.

Tasks

• Require explicit lsp invocation and remove the implicit top-level language-server entry point.
• Update alexandrite-vscode to 0.1.0 with this breaking change.

Target release: 0.1.0.