Prepare first downloadable release: install export templates, build 0.1.0 binaries, add publish helper

- Install Godot 4.3 export templates locally and fix macOS export
  (enable rendering/textures/vram_compression/import_etc2_astc)
- Build Linux/Windows/macOS artifacts into build/ via tools/build_releases.sh;
  Linux binary passes headless smoke test
- Add tools/publish_release.sh (creates Gitea release + uploads assets with a token)
- TODO: mark build/install steps done; publishing v0.1.0 + link verification
  remain as the single action blocker (needs GITEA_TOKEN)

docs/RELEASING.md

@@ -54,6 +54,18 @@ Artifacts are written to `build/`:
 
 The repository lives at `https://git.allucanget.biz/zwitschi/security-game`.
 
+Preferred path — use the helper script with a token:
+
+```bash
+GITEA_TOKEN=your_api_token ./tools/publish_release.sh 0.1.0
+```
+
+The script creates the release from `project.godot`'s `config/version`, uploads
+all three `build/` artifacts, and prints the release URL. The token needs only
+`write:repository` scope on the Gitea host.
+
+Manual alternative:
+
 ### Via the web UI
 
 1. Create a **New Release** with tag `v<version>`.