Add keyboard play: arrows/WASD/hjkl focus, Enter/Space flips

Focus ring appears on the first key press and hides when the mouse moves.
Enter also triggers Play Again on the win panel.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/memory/memory.odin

@@ -56,6 +56,8 @@ elapsed: f32
 resolve_timer: f32
 win_t: f32 // fades in the win panel
 restart_requested: bool
+focus: int           // card selected with the keyboard
+keyboard_active: bool // show the focus ring (hidden again when the mouse moves)
 
 // Deals a new game and renders the card faces. Needs the window to exist.
 start :: proc(deck_id: decks.Deck_Id, game_difficulty: Difficulty) {
@@ -112,6 +114,7 @@ deal :: proc(deck_id: decks.Deck_Id, game_difficulty: Difficulty) {
     resolve_timer = 0
     win_t = 0
     restart_requested = false
+    focus = 0
 }
 
 active_cards :: proc() -> []card.Card {
@@ -146,6 +149,42 @@ select_card :: proc(i: int) -> bool {
     return true
 }
 
+// Moves the keyboard focus within the grid, clamped at the edges
+move_focus :: proc(dx, dy: int) {
+    col := clamp(focus % layout.cols + dx, 0, layout.cols - 1)
+    row := clamp(focus / layout.cols + dy, 0, layout.rows - 1)
+    focus = row * layout.cols + col
+}
+
+@(private)
+key_pressed :: proc(keys: ..raylib.KeyboardKey) -> bool {
+    for key in keys {
+        if raylib.IsKeyPressed(key) || raylib.IsKeyPressedRepeat(key) { return true }
+    }
+    return false
+}
+
+// Arrows, WASD or vim keys move the focus; Enter or Space flips the focused card
+@(private)
+handle_keyboard :: proc() {
+    if raylib.GetMouseDelta() != {} { keyboard_active = false }
+
+    dx, dy := 0, 0
+    if key_pressed(.LEFT, .A, .H)  { dx -= 1 }
+    if key_pressed(.RIGHT, .D, .L) { dx += 1 }
+    if key_pressed(.UP, .W, .K)    { dy -= 1 }
+    if key_pressed(.DOWN, .S, .J)  { dy += 1 }
+    if dx != 0 || dy != 0 {
+        // The first key press only reveals the focus ring
+        if keyboard_active { move_focus(dx, dy) }
+        keyboard_active = true
+    }
+    if raylib.IsKeyPressed(.ENTER) || raylib.IsKeyPressed(.SPACE) {
+        keyboard_active = true
+        select_card(focus)
+    }
+}
+
 @(private)
 resolve :: proc() {
     a, b := &cards[first], &cards[second]
@@ -180,6 +219,7 @@ update :: proc(dt: f32) {
     }
 
     for &c in active_cards() { card.update(&c, dt) }
+    if state != .OVER { handle_keyboard() }
 
     switch state {
     case .WAITING, .FIRST:
@@ -221,7 +261,7 @@ draw :: proc() -> themes.Screen {
     }
 
     for &c, i in active_cards() {
-        card.draw(&c, theme, can_pick(i))
+        card.draw(&c, theme, can_pick(i), focused = keyboard_active && i == focus && state != .OVER)
     }
 
     if state == .OVER {
@@ -256,7 +296,7 @@ draw_win_panel :: proc() -> Maybe(themes.Screen) {
     if win_t < 1 { return nil }
     button_w: f32 = 200
     button_y := panel.y + panel_h - 100
-    if ui.button({cx - button_w - 10, button_y, button_w, 60}, "Play Again", theme.primary) {
+    if ui.button({cx - button_w - 10, button_y, button_w, 60}, "Play Again", theme.primary, hotkey = .ENTER) {
         restart_requested = true
     }
     if ui.button({cx + 10, button_y, button_w, 60}, "Menu", theme.ink) {