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>

justfile

@@ -0,0 +1,43 @@
+name := "HanjaKanaMun"
+build_dir := "build"
+
+# List available recipes
+default:
+    @just --list
+
+# Debug build
+build:
+    odin build . -vet -debug -out:{{name}}
+
+# Build and run (debug)
+run:
+    odin run . -vet -debug -out:{{name}}
+
+# Type-check with vet, no binary
+check:
+    odin check . -vet
+
+# Run the test suite (single-threaded: the tests share the memory game's global state)
+test:
+    mkdir -p {{build_dir}}
+    odin test tests -vet -define:ODIN_TEST_THREADS=1 -out:{{build_dir}}/tests
+
+# Optimized build into build/, with the assets it needs at runtime
+release:
+    mkdir -p {{build_dir}}/{{name}}
+    odin build . -vet -o:speed -out:{{build_dir}}/{{name}}/{{name}}
+    cp -R assets {{build_dir}}/{{name}}/
+
+# Release build packed as build/<name>_<version>_<os>_<arch>.tar.gz
+package version="dev": release
+    tar -czf {{build_dir}}/{{name}}_{{version}}_{{os()}}_{{arch()}}.tar.gz -C {{build_dir}} {{name}}
+    @echo "{{build_dir}}/{{name}}_{{version}}_{{os()}}_{{arch()}}.tar.gz"
+
+# Format all Odin files with odinfmt (settings in odinfmt.json)
+fmt:
+    odinfmt -w .
+
+# Remove build output
+clean:
+    if [ -d {{build_dir}} ]; then rm -r -- {{build_dir}}; fi
+    rm -f -- {{name}}