Various WIP: CLI REPL, Sqlite, MCP, TreeView, FSP, etc.

[StachuDotNet]

Various work I've had locally:

• progress on our CLI UX / REPL
• lots of fun with Sqlite
  • some backend (esp cloud) functionality has been commented out accordingly; needs to be fixed at some point, but probably ok if we leave some commented while we focus on a local-friendly CLI release
• pulling back in a "TreeView" in VS Code
• start to scaffold support for (and one impl of) a MCP Server, similar to our support for LSP Servers
• pulled in Ocean's work on FileSystemProvider support for VS Code

Frankly, much of this is half-done, as I was jumping around and distracted by non-tech work :) But, good to get this out of my head.

The MCP work is commented out (folders have underscores at the start of their names). It was close to building, but not yet tested.

[StachuDotNet]

This PR was becoming super messy; split into a few smaller ones, pairing w/ @OceanOak