Implement ActionCable for Live Game Updates

[frogr]

Acceptance Criteria

• Stats update without refresh when damaged/healed
• Location changes broadcast to all players in area
• Combat mode triggers UI changes
• Notifications appear and auto-dismiss

Technical Requirements

• Create GameChannel with player-specific streams
• Handle update types: stat_update, location_change, combat_update
• Smooth animations for stat changes (500ms transitions)
• Notification stack in top-right corner