Make card elements focusable via tabindex="0" and add arrow-key focus cycling, Enter/Space activation, so the game board is operable without a mouse. Currently cards are non-focusable divs and all keyboard shortcuts require prior mouse selection.

Context
Cards are created as plain <div> elements with no tabindex attribute, making them invisible to keyboard navigation. The existing keyboard handler in keyboard.js only operates on a selectedCard variable that is set exclusively by the mouse grab event in card.js. A keyboard-only user cannot select, flip, rotate, or interact with any card. Adding tabindex="0" to cards, arrow-key focus cycling between .game-card elements, and Enter/Space as activation keys (flip) closes this accessibility gap with a bounded change to two files.

Affected Files

• src/scripts/card.js:7 — Add tabindex="0" to the cardElement created in createCard
• src/scripts/card.js:29 — Add a focus event listener that calls selectCard so keyboard focus and selection stay in sync
• src/scripts/keyboard.js:27 — Add ArrowLeft/ArrowRight cases to cycle focus between .game-card elements, and Enter/Space to toggle flip
• src/scripts/keyboard.test.js — Add tests for arrow-key focus cycling and Enter/Space flip activation

Requirements

• Every card element created by createCard has tabindex="0" so it appears in the tab order
• Pressing ArrowRight moves focus to the next .game-card sibling in DOM order; ArrowLeft moves to the previous
• Arrow-key navigation wraps around — pressing right on the last card focuses the first, and vice versa
• Pressing Enter or Space on a focused card toggles its flipped class, matching the F key behavior
• Focusing a card via Tab or arrow keys calls selectCard so R/F/Delete shortcuts operate on the focused card
• The text-input guard (INPUT/TEXTAREA focus check) applies to all new key bindings
• Tests verify: arrow-key cycling, wrap-around, Enter/Space flip, focus-sets-selection, input guard

Verification

• grep -n 'tabindex' src/scripts/card.js
• grep -n 'Arrow' src/scripts/keyboard.js
• npm test -- --reporter=verbose 2>&1 | grep -iE 'arrow|enter|space|tabindex|focus'
• npm test

Not In Scope

• Do not add ARIA live regions or screen-reader announcements
• Do not change the visual styling of focused cards beyond what the browser provides natively
• Do not add keyboard navigation for tokens or decks in this issue

Evidence

• src/scripts/card.js:7 — cardElement is created via document.createElement("div") with no tabindex — it is not keyboard-focusable
• src/scripts/keyboard.js:27-44 — Switch statement handles only r, R, f, F, Delete, Escape — no ArrowLeft, ArrowRight, Enter, or Space cases
• src/scripts/card.js:33-36 — The grab event listener calls selectCard, but grab is only dispatched by mouse mousedown — no keyboard path sets selection

_{Arasaka Queue Planning Division.}