Add desktop binary exports to the CI pipeline

Export win-x86, win-x64, linux-x64 and mac-universal builds headless
from the godot-builder image and upload them as ReleaseAssets
(<project>-<version>-<target>.zip, single root folder). Mac is one
universal (intel + arm) build with Godot's built-in ad-hoc codesign;
per-arch export is not possible with the official export templates.
ETC2 ASTC texture import is enabled because the arm64 slice requires it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.woodpecker.yaml

@@ -9,6 +9,7 @@ steps:
     image: git.teletypegames.org/internal/godot-builder:4.7.1
     commands:
       - make ci-export
+      - make ci-binaries
 
   - name: artifact
     image: alpine