Add public auth public coverage

[mikeclark206]

Summary

Adds non-secret auth-related coverage for the Discogs login page and unauthenticated account access.

Changes

• Added LoginPage page object
• Added login page smoke test
• Added negative auth test for unauthenticated access to account area
• Updated test scenario documentation
• Restored npm test scripts for local execution
• Stabilized search submission by confirming input visibility, focus, and value before pressing Enter

Validation

• Ran auth tests locally in Chromium
• Ran full test suite locally with npm test
• Confirmed all tests pass

Notes

This slice intentionally does not use credentials or saved auth state. Authenticated collection coverage can be added separately using secure environment variables and Playwright storage state.