Add e2e tests for sidebar Scan button behavior with interpreter detection

[zackverham]

Context

PR #3704 replaced the Go /interpreters endpoint with a TypeScript interpreter detection module. A bug was found where relative projectDir paths caused requirements.txt detection to fail, making the sidebar erroneously show the Scan button for projects that should have been fully configured. This was fixed by resolving projectDir to an absolute path in state.ts.

Unit and integration tests were added to cover the path resolution and the interpreter detection pipeline, but there are no e2e tests validating the sidebar's end-to-end behavior — i.e., that the Scan button does not appear when a project has a valid requirements.txt and a Python interpreter is available.

What to test

Add Cypress e2e tests that validate:

1. Python project with requirements.txt: The sidebar should display the detected Python version and requirements.txt as the package file — the Scan button should not appear.
2. R project with renv.lock/DESCRIPTION: The sidebar should display the detected R version — the Scan button should not appear.
3. Project with no package file: The Scan button (or equivalent prompt) should appear, since interpreter defaults are incomplete.

References

• Fix commit: d83eec1 (PR Wire TypeScript interpreter module into state.ts, remove Go endpoint #3704)
• Interpreter module: extensions/vscode/src/interpreters/
• State call sites: extensions/vscode/src/state.ts — getSelectedConfiguration() and refreshConfigurations()
• Existing e2e setup: test/e2e/