fix(auth): commit browser-login brand assets needed by login page

icon.svg and favicon.ico under web/static/brand are read at runtime by
auth/browser_login_page to embed branding in the OAuth callback HTML, but the
whole web/static tree is gitignored — so CI's clean checkout lacked them and
test_openai_callback_html_* failed with FileNotFoundError (passed locally only
because the files exist on disk). Force-add the two required assets so the
feature and its tests work from a fresh clone.

Author: elkaix