Pass the environment directory to uv package commands

[Copilot]

UV-backed package operations were constructed with environment.execInfo.run.executable. For symlinked virtual environments (e.g. Pipenv), that executable can resolve to a uv-managed base interpreter, so uv pip install --python <exe> operated on the externally managed base interpreter instead of the selected environment.

uv accepts an environment directory as its --python target, so the fix is to hand UV commands environment.environmentPath.fsPath at the pip/uv boundary. Ordinary pip commands still need the interpreter executable.

Changes

• src/managers/builtin/commands/factory.ts: when shouldUseUv(...) selects uv, construct the UV command with a copy of the options whose pythonExecutable is environmentPath. Pip commands keep the original options.
• src/test/managers/builtin/commands.unit.test.ts: stub shouldUseUv once in the existing setup and add regression coverage that UV install/uninstall/list/direct-names all pass the environment directory after --python and never the base interpreter, and that pip still runs runPython with the original interpreter.

if (await shouldUseUv(options.log, environmentPath)) {
    // uv accepts an environment directory as its `--python` target. A symlinked
    // environment executable (for example Pipenv) can resolve to the externally
    // managed base interpreter, so passing the environment directory preserves
    // the environment boundary. Pip commands keep using the interpreter itself.
    return { kind: 'uv', command: new UvCommand({ ...options, pythonExecutable: environmentPath }) };
}
return { kind: 'pip', command: new PipCommand(options) };

Fixing this centrally covers every factory-created UV operation without touching each command class. Call sites were reviewed: UvVersionCommand (uv --version) and UvAvailableVersionsCommand (uv tool run pip index versions …) don't reference pythonExecutable in their arguments, so they're unaffected.

This adapts the intent of #1673 to the command-class refactor merged later in #1686.

[Eduardo Villalpando Mello (edvilme)]

Fixes #1674