[Feature] Shareable comparison and player links

[grovecj]

Summary

Generate shareable URLs for player stats and comparison views so users can share results with friends.

Details

URL Structure

• Player stats: /player/{platform}/{gamertag} (already routable)
• Comparison: /compare?p=uno:player1,xbl:player2,psn:player3
• Squad view: /squad/{squadId}

Share Features

• Copy link button on player stats page and comparison page
• Uses navigator.clipboard.writeText() with fallback
• Naive UI notification confirming "Link copied!"
• URL updates reactively as players are added/removed from comparison

Router Integration

• Comparison page reads p query param on mount, parses players, fetches stats
• Player add/remove updates the URL query params (using router.replace)
• Browser back/forward works correctly with comparison state

Acceptance Criteria

• Copy link button on stats and comparison pages
• Comparison URL encodes all selected players
• Opening a shared comparison URL loads all players correctly
• Browser history navigation works with comparison state