Fix dashboard overflow and add responsive UI CI guard

[mergemaven11]

What this fixes

• Prevent authenticated BragStack content from extending past the viewport beside the fixed sidebar.
• Add global min-width/max-width and long-content wrapping guardrails for the dashboard and authenticated shell.
• Add a real-Chrome responsive layout audit across phone, tablet, narrow desktop, desktop, and wide desktop sizes.
• Fail Frontend CI if authenticated content or dashboard cards are clipped on the right or create horizontal overflow.
• Capture failure screenshots for 3 days when the responsive UI guard fails.

Why

The production dashboard was visibly cut off on the right. This PR makes that class of regression a CI failure instead of something we discover manually after deploy.

Coverage

Responsive browser checks run at 360, 390, 768, 1024, 1440, and 1920px widths across Dashboard, Accomplishments, Impact Receipts, and Profile.