Tasks

• [x] Add responsive CSS breakpoint for narrow dashboard screens
• [x] Collapse spec browser grid to a single-column mobile layout
• [x] Make spec list horizontally scrollable on mobile
• [x] Stack diff columns and scenario before/after blocks on mobile
• [x] Wrap long spec paths, requirement names, scenario names, step text, and card titles
• [x] Reduce mobile modal/page padding and prevent page-level horizontal overflow
• [x] Add OpenSpec coverage for mobile-friendly spec layout