feat(interpreters): add an existing Python virtual environment as an interpreter (#2076)

Refs #1907

Add Python Interpreter → Existing environment: Browse picks the environment folder, which is resolved right away (pyvenv.cfg, bin/python or Scripts\python.exe) and added to the interpreter list as "Python X.Y (<env name>)", then remembered. Picking the folder rather than the executable keeps the environment's identity, since the native file picker resolves the venv's python symlink to the base interpreter. Works for `python -m venv` and uv environments; a broken environment shows an error instead of being added. Probing runs off the command thread.

Co-authored-by: Inf1mum <[email protected]>

src/ui/Select.tsx

@@ -20,6 +20,7 @@ export interface SelectOption<V extends string = string> {
 }
 
 export interface SelectProps<V extends string = string> {
+  id?: string;
   value: V | null;
   options: readonly SelectOption<V>[];
   onChange: (value: V) => void;
@@ -177,6 +178,7 @@ export function Select<V extends string = string>({
     <>
       <button
         ref={triggerRef}
+        id={aria.id}
         type="button"
         aria-haspopup="listbox"
         aria-expanded={open}