Deck Builder UI + Validation

[Doberjohn]

Part of #204

Description

Build the core deck building interface with rule enforcement.

Requirements

• Card add/remove interface (search/browse to add, click/button to remove)
• Quantity controls (increment/decrement per card)
• 4-copy maximum — prevent adding more than 4 of any card
• 2-color maximum — once 2 ink colors are in the deck, grey out / disable cards of other colors
• 60-card soft limit — allow more than 60 cards but show a warning (not a hard rule in Lorcana)
• Deck card list with quantities, grouped or sortable
• Deck stats summary (card count, color distribution, cost curve)

UX Notes

• Integration with existing card browse/search for adding cards
• Clear visual feedback when rules are violated (4-copy, 2-color)
• Responsive: works on both desktop and mobile

Phase

Phase 2 (weeks 3-4)

Files

• apps/web/src/features/deck/ — new feature directory