Add screen fade-in and card deal-in animations

Cards slide in one after another when a game starts and can't be picked
until they have landed.

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

main.odin

@@ -13,6 +13,8 @@ import screens "src/screens"
 import themes "src/themes"
 import ui "src/ui"
 
+TRANSITION_SPEED :: 4 // screen fade-ins per second
+
 // Where Escape takes you from each screen (nil = quit)
 parent_screen :: proc(screen: themes.Screen) -> Maybe(themes.Screen) {
     switch screen {
@@ -53,6 +55,7 @@ main :: proc() {
     if saved, ok := reflect.enum_from_name(memory.Difficulty, profile.data.difficulty); ok {
         difficulty = saved
     }
+    transition_t: f32 = 1 // fades the screen in from the background color
     running := true
     for running && !raylib.WindowShouldClose() {
         dt := raylib.GetFrameTime()
@@ -60,6 +63,7 @@ main :: proc() {
         if raylib.IsKeyPressed(.ESCAPE) {
             if parent, ok := parent_screen(screen).?; ok {
                 screen = parent
+                transition_t = 1
             } else {
                 running = false
             }
@@ -90,6 +94,11 @@ main :: proc() {
         case .MEMORY:
             next = memory.draw()
         }
+        if transition_t > 0 {
+            alpha := transition_t * transition_t
+            raylib.DrawRectangle(0, 0, themes.SCREEN_WIDTH, themes.SCREEN_HEIGHT, raylib.Fade(themes.MENU_BACKGROUND, alpha))
+            transition_t = max(transition_t - dt * TRANSITION_SPEED, 0)
+        }
         ui.end_frame()
         raylib.EndDrawing()
         free_all(context.temp_allocator)
@@ -99,6 +108,7 @@ main :: proc() {
         if deck, ok := start_deck.?; ok {
             memory.start(deck, difficulty)
         }
+        if next != screen { transition_t = 1 }
         screen = next
     }
 }