Split marketplace definition into two plugins: skills-only + ty LSP-only

[TyceHerrman]

Summary

Proposing splitting the current plugin in two:

1. astral (skills only: uv, ruff, ty guidance)
2. ty-lsp (LSP only: ty language server)

Problem

Users cannot selectively disable the ty LSP if using a different lsp plugin while keeping the skills.

Proposed change

• Create a skills-only plugin.
• Introduce a separate ty-lsp plugin that contains only:
  • lspServers.ty.command = "uvx"
  • lspServers.ty.args = ["ty@latest", "server"]
  • Python file extensions mapping (.py, .pyi).
• Publish both plugins in the Astral marketplace.
• Update docs to show independent install paths and migration guidance.