Enhance pool expiry messaging with urgency levels and relative dates

[DomDom3333]

Summary

Improved the pool expiry notification system to provide more granular urgency indicators and human-friendly relative date formatting. The expiry banner now displays contextual messaging based on how soon the pool will expire, with distinct visual styling for different urgency levels.

Key Changes

• Backend logic: Added BuildExpiryLabel() method to generate human-readable relative dates (e.g., "today", "tomorrow", "in 3 days", "in 2 weeks")
• Urgency classification: Added BuildExpiryUrgency() method that categorizes expiry timeframes into four levels:
  • critical: ≤7 days (red styling, warning emoji, action text)
  • warning: ≤30 days (orange styling)
  • notice: ≤90 days (yellow styling)
  • info: >90 days (blue styling)
• Model properties: Added ExpiryLabel and ExpiryUrgency properties to GalleryModel
• UI enhancement: Redesigned expiry banner with:
  • Flexible layout using flexbox for better responsiveness
  • Contextual emoji icon (⚠️ for critical, 🗓 for others)
  • Relative date display in smaller, muted text
  • Urgent call-to-action text only shown for critical expiry
• Styling: Added comprehensive CSS for four urgency levels with light and dark theme support, maintaining visual consistency with existing banner styles

Implementation Details

• The expiry check now always evaluates the expiry date when present, not just when it's within 7 days
• Relative date calculations use TimeSpan.TotalDays and TotalHours for accurate thresholds
• Plural handling for day/week/month labels (e.g., "1 day" vs "2 days")
• Color palette chosen for accessibility and visual hierarchy across both light and dark themes

https://claude.ai/code/session_019sA2fUMbEuMe8QTgfJanif