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>

.gitea/workflows/gitea-build.yaml

@@ -0,0 +1,53 @@
+#
+# .gitea/workflows/gitea-build.yaml
+#
+# Builds and tests on every push and pull request to main and develop.
+#
+
+name: "Build and Test"
+on:
+  push:
+    branches: [main, develop]
+  pull_request:
+    branches: [main, develop]
+
+env:
+  ODIN_VERSION: dev-2026-09
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Install System Dependencies
+        run: |
+          SUDO=""; command -v sudo >/dev/null && SUDO=sudo
+          $SUDO apt-get update
+          # clang links Odin programs; raylib needs X11 on Linux
+          $SUDO apt-get install -y --no-install-recommends clang libx11-dev curl ca-certificates
+
+      - name: Install Odin
+        run: |
+          curl -fsSL -o odin.tar.gz https://github.com/odin-lang/Odin/releases/download/$ODIN_VERSION/odin-linux-amd64-$ODIN_VERSION.tar.gz
+          mkdir -p "$HOME/odin"
+          tar -xzf odin.tar.gz -C "$HOME/odin" --strip-components=1
+          echo "$HOME/odin" >> "$GITHUB_PATH"
+
+      - name: Install just
+        run: |
+          mkdir -p "$HOME/.local/bin"
+          curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to "$HOME/.local/bin"
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+
+      - name: Check
+        run: |
+          odin version
+          just check
+
+      - name: Test
+        run: just test
+
+      - name: Build
+        run: just release