Add Gitea release workflow: per-platform wheel builds, then publish to PyPI

Matrix job builds and tests wheels on linux/macos/windows (no Gitea
release, unlike mediahive); publish job uploads the merged dist/ to PyPI
only after all platforms succeed. release.py gains --no-upload for the
matrix jobs.

.gitignore

@@ -8,4 +8,5 @@
 /src/aeg/_aegis*.pyd
 __pycache__
 !.gitignore
+!.gitea/
 !.gitmodules