Add Playwright test S7 to verify that the story footer back link
renders with the .back-pill class for consistent design system styling.
This test scrolls past the hero to reveal the footer and checks both
class presence and text content.
Also update user submodule pointer to include the back-pill application.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WPJztrVGbwic2xTG7G9fjM
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