Add release environment to release workflow

Restricts release workflow to protected branches only.
Environment managed via terraform-github.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: matthewtoma-idme

.github/workflows/release.yml

@@ -16,8 +16,7 @@ on:
 jobs:
   release:
     runs-on: ubuntu-latest
-    # TODO: Add `environment: release` after testing, then create the environment
-    # in repo Settings > Environments with "Protected branches only" deployment policy
+    environment: release
     permissions:
       contents: write
       packages: write