Add custom ruff/ty binary paths with structured resolution

[manzt]

Closes #408

Users in offline or restricted environments cannot use the extension's managed ruff/ty language servers because the uv pip install fallback requires internet access. This adds two new settings (marimo.ruff.path and marimo.ty.path) and a companion extension discovery mechanism so these users can point to locally-installed binaries instead.

New settings

• marimo.ruff.path — absolute path to a custom ruff binary
• marimo.ty.path — absolute path to a custom ty binary

Leave empty (default) to use automatic discovery.

Resolution strategy

Binary resolution follows this priority for both ruff and ty:

1. User-configured path — marimo.ruff.path / marimo.ty.path
2. Companion extension — checks the charliermarsh.ruff or
   astral-sh.ty extension's own path setting (ruff.path /
   ty.path), then its bundled binary at
   <extensionPath>/bundled/libs/bin/<binary>
3. uv pip install — existing behavior, unchanged

Each candidate is validated by running <binary> --version and checking it meets the minimum version (ruff >= 0.15.6, ty >= 0.0.23). If validation fails at any tier, resolution falls through to the next.

The resolution pipeline is generic: resolveBinary() accepts an ordered list of ResolutionSource values and a fallback, tries each in sequence, and returns a BinarySource tagged enum describing where the binary came from:

type BinarySource = Data.TaggedEnum<{
  UserConfigured: { path: string };
  CompanionExtension: {
    extensionId: string;
    path: string;
    kind: "configured" | "bundled";
  };
  UvInstalled: { path: string };
}>;

[nojaf]

Hi @manzt, we are running into this problem.
We have a /etc/uv/uv.toml with

index-url = "https://our.domain.internal/api/pypi/pypi-all/simple"
python-install-mirror = "https://our.domain.internal/generic-github-remote/astral-sh/python-build-standalone/releases/download"
native-tls = true

Will this PR use https://docs.astral.sh/uv/reference/settings/#index-url and not override it when

marimo-lsp/extension/src/services/Uv.ts

Line 374 in 7ca6754

UV_DEFAULT_INDEX: "https://pypi.org/simple/",

gets set?

Related issue #437

[manzt]

This PR doesn't fix the UV_DEFAULT_INDEX override (#437). That's a separate issue. But it does let you bypass uv pip install entirely for ruff/ty.

The easiest path forward: install the charliermarsh.ruff and astral-sh.ty companion extensions. The marimo extension will discover their bundled binaries automatically. Alternatively, install the binaries yourself and point to them:

{
  "marimo.ruff.path": "/usr/local/bin/ruff",
  "marimo.ty.path": "/usr/local/bin/ty"
}