Add justfile, ols/odinfmt config, tests and Gitea workflows; drop odin.json

- justfile with build/run/check/test/release/package/fmt/clean recipes
- ols.json and odinfmt.json for neovim (ols)
- Tests for memory game rules and card animation; memory.deal and
  memory.select_card split out so logic is testable without a window
- Gitea workflows: build+test on main/develop, package and upload to the
  generic package registry on version branches
- Game changes to the executable's directory so packaged builds find assets

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

main.odin

@@ -24,6 +24,8 @@ main :: proc() {
     raylib.InitWindow(themes.SCREEN_WIDTH, themes.SCREEN_HEIGHT, "HanjaKanaMun")
     defer raylib.CloseWindow()
     raylib.SetExitKey(.KEY_NULL)
+    // Assets are loaded relative to the executable, so it can be started from anywhere
+    raylib.ChangeDirectory(raylib.GetApplicationDirectory())
     raylib.SetTargetFPS(60)
 
     raylib.InitAudioDevice()