Add share functionality to tip split calculation page

[bradydibble]

Summary

Added a share button to the tip split calculation share page that allows users to share the tip distribution details via the native share API or copy to clipboard as a fallback.

Key Changes

• New buildShareText() function: Formats the tip split data (date, shift, gross tips, fees, pools, and individual distributions) into a readable text format
• New shareViaMessenger() function: Implements sharing logic that:
  • Uses the native Web Share API when available (for mobile/supported browsers)
  • Falls back to copying formatted text to clipboard on unsupported browsers
  • Shows "Copied!" feedback message for 2 seconds after clipboard copy
• New share button UI: Added a styled button with share icon below the tip split card
  • Displays dynamic text (either "Share via Messenger" or "Copied!" feedback)
  • Includes hover and active state animations
  • Responsive design with proper spacing and alignment

Implementation Details

• Uses Svelte's $state for managing the copyFeedback message
• Share text includes all relevant information: date, shift type, gross tips, fees, pools, individual distributions, and total
• Gracefully handles cases where the Web Share API is unavailable or user cancels the share action
• Button styling uses CSS variables for consistency with the existing design system

https://claude.ai/code/session_01SKaGpS6Kr6TTNUrTGmWLrU