ci: add GitHub and Codeberg release build workflows

Add tag-triggered CI that builds and publishes the linux/amd64,
linux/arm64, and windows/amd64 release binaries on both forges.

- scripts/ci-build-release.sh: shared, Docker-free build+package for all
  three targets (Windows cross-compiled via MinGW), reused by both
  workflows so the build logic lives in one place.
- .github/workflows/release.yml: GitHub Actions, publishes via
  softprops/action-gh-release using the built-in token.
- .forgejo/workflows/release.yml: Forgejo Actions for Codeberg, publishes
  via forgejo-release using a RELEASE_TOKEN secret.
- .gitattributes: force LF on workflow YAML so bash run: blocks don't
  break on Linux runners.
- docs/DEVELOPMENT.md: document the tag -> release flow and token setup.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitattributes

@@ -1,3 +1,8 @@
 # Keep shell scripts LF even on Windows checkouts so bash on Linux hosts
 # doesn't choke on trailing CRs (e.g. "set: pipefail: invalid parameter name").
 *.sh text eol=lf
+
+# CI workflow YAML embeds shell in `run:` blocks that Linux runners execute with
+# bash, so keep these LF for the same reason as the shell scripts above.
+.github/workflows/*.yml text eol=lf
+.forgejo/workflows/*.yml text eol=lf