Restructure into themed screens with flag card backs, real font, flip animation and sound

- Replace the bogus DroidSansJapanese.ttf (an HTML page) with M PLUS Rounded 1c,
  loaded with LoadFontEx and explicit kana codepoints
- Theme struct per language with flag-based card backs (Hinomaru, Taegukgi, Trairong)
- Card art rendered to textures so the flip squashes the whole card
- Synthesized flip/match/mismatch/win/click sounds (new audio package)
- Shared ui package for text and buttons; Screen enum replaces i32 ids
- Kana <-> romaji pairs drawn from all 46 basic hiragana

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

main.odin

@@ -1,56 +1,77 @@
 package main
 
 import raylib "vendor:raylib"
-import themes "src/themes"
-import screens "src/screens"
-import memory "src/memory"
 import assets "src/assets"
+import audio "src/audio"
+import card "src/card"
+import memory "src/memory"
+import screens "src/screens"
+import themes "src/themes"
+import ui "src/ui"
 
-current_screen: i32 = themes.MAIN_MENU
-mouse_x: i32
-mouse_y: i32
+// Where Escape takes you from each screen (nil = quit)
+parent_screen :: proc(screen: themes.Screen) -> Maybe(themes.Screen) {
+    switch screen {
+    case .MAIN_MENU:       return nil
+    case .JAPANESE_MEMORY: return .JAPANESE_MENU
+    case .JAPANESE_MENU, .KOREAN_MENU, .THAI_MENU: return .MAIN_MENU
+    }
+    return nil
+}
 
 main :: proc() {
-    raylib.InitWindow(themes.SCREEN_WIDTH, themes.SCREEN_HEIGHT, cstring("HanjaKanaMun"))
+    raylib.SetConfigFlags({.MSAA_4X_HINT, .VSYNC_HINT})
+    raylib.InitWindow(themes.SCREEN_WIDTH, themes.SCREEN_HEIGHT, "HanjaKanaMun")
     defer raylib.CloseWindow()
-    raylib.SetExitKey(raylib.KeyboardKey.KEY_NULL)
-    
+    raylib.SetExitKey(.KEY_NULL)
+    raylib.SetTargetFPS(60)
+
+    raylib.InitAudioDevice()
+    defer raylib.CloseAudioDevice()
+    audio.load()
+    defer audio.unload()
+
     assets.load_fonts()
     defer assets.unload_fonts()
-    
-    raylib.SetTargetFPS(60)
-    memory.init_memory_game()
-    
-    for !raylib.WindowShouldClose() {
-        mouse_x = raylib.GetMouseX()
-        mouse_y = raylib.GetMouseY()
-        
-        if raylib.IsKeyPressed(raylib.KeyboardKey.ESCAPE) {
-            current_screen = themes.MAIN_MENU
-        }
-        
-        if current_screen == themes.JAPANESE_MEMORY {
-            delta_time := raylib.GetFrameTime()
-            memory.update_memory_game(delta_time, mouse_x, mouse_y)
-        }
-        
-        raylib.BeginDrawing()
-        
-        if current_screen == themes.MAIN_MENU {
-            current_screen = screens.draw_main_menu(mouse_x, mouse_y)
-        } else if current_screen == themes.JAPANESE_SCREEN {
-            current_screen = screens.draw_japanese_screen(mouse_x, mouse_y)
-            if current_screen == themes.JAPANESE_MEMORY {
-                memory.init_memory_game()
+    card.load_art()
+    defer card.unload_art()
+    defer memory.unload()
+
+    screen := themes.Screen.MAIN_MENU
+    running := true
+    for running && !raylib.WindowShouldClose() {
+        dt := raylib.GetFrameTime()
+
+        if raylib.IsKeyPressed(.ESCAPE) {
+            if parent, ok := parent_screen(screen).?; ok {
+                screen = parent
+            } else {
+                running = false
             }
-        } else if current_screen == themes.JAPANESE_MEMORY {
-            current_screen = memory.draw_memory_game(mouse_x, mouse_y)
-        } else if current_screen == themes.KOREAN_SCREEN {
-            current_screen = screens.draw_korean_screen(mouse_x, mouse_y)
-        } else if current_screen == themes.THAI_SCREEN {
-            current_screen = screens.draw_thai_screen(mouse_x, mouse_y)
         }
-        
+
+        if screen == .JAPANESE_MEMORY {
+            memory.update(dt)
+        }
+
+        raylib.BeginDrawing()
+        ui.begin_frame()
+        next := screen
+        switch screen {
+        case .MAIN_MENU:       next = screens.main_menu()
+        case .JAPANESE_MENU:   next = screens.japanese_menu()
+        case .JAPANESE_MEMORY: next = memory.draw()
+        case .KOREAN_MENU:     next = screens.korean_menu()
+        case .THAI_MENU:       next = screens.thai_menu()
+        }
+        ui.end_frame()
         raylib.EndDrawing()
+
+        // Start a fresh game when entering the memory screen (outside of drawing,
+        // because building card faces renders into textures)
+        if next == .JAPANESE_MEMORY && screen != .JAPANESE_MEMORY {
+            memory.start(themes.JAPAN)
+        }
+        screen = next
     }
 }