Add Windows cross-build and Gitea release; share CI setup

- just windows-deps / windows / package-windows: cross-compile with Odin
  objects + lld-link against an xwin SDK, static VC runtime
- Release workflow runs on v* tags, builds Linux and Windows packages,
  uploads them to the package registry and creates a Gitea release
- Shared toolchain setup as a local composite action

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

.gitea/workflows/gitea-build.yaml

@@ -1,7 +1,7 @@
 #
 # .gitea/workflows/gitea-build.yaml
 #
-# Builds and tests on every push and pull request to main and develop.
+# Checks, tests and builds on every push and pull request to main and develop.
 #
 
 name: "Build and Test"
@@ -11,9 +11,6 @@ on:
   pull_request:
     branches: [main, develop]
 
-env:
-  ODIN_VERSION: dev-2026-09
-
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -21,25 +18,8 @@ jobs:
       - 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: Setup Toolchain
+        uses: ./.gitea/actions/setup
 
       - name: Check
         run: |