- Copy logo_dark.png and logo_white.png from go-backend/static into backend/static
- Replace minimal 62-line auth.css with 828-line extraction from go-backend/static/styles.css
- Sections: login-screen shell, animated background (bg-01..35, size/opacity utilities), card wrapper, card internals, gsi-material-button, legacy auth-provider controls, 66 keyframe definitions, animate-* utility classes
- Added display:block and text-decoration:none to .gsi-material-button for the anchor variant
- Does NOT include .app-shell or .dashboard-shell rules
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