Add hover effect to reveal accent colors on upcoming timeline cards

[yepzdk]

Summary

• Adds hover effect to upcoming timeline cards that reveals their accent colors (pink/blue)
• Transitions smoothly from gray styling to accent color on hover
• Includes transition support for dot, connector line, accent bar, status badge, link button, subtitle, and date wrapper
• Respects prefers-reduced-motion by disabling transitions when reduced motion is preferred

Test plan

• Navigate to a project with a timeline that has upcoming cards with accent colors
• Hover over an upcoming card with accent-pink class - should reveal pink styling
• Hover over an upcoming card with accent-blue class - should reveal blue styling
• Verify color transitions are smooth (0.2s ease)
• Test in both vertical and horizontal timeline views
• Test with prefers-reduced-motion: reduce enabled in browser/OS settings

Fixes #610

🤖 Generated with Claude Code

[yepzdk]

It should not only work on accents colors. We need it for the green cards also (Hearing, Dialog etc.)