Gitea prefers .gitea/ISSUE_TEMPLATE/ and .gitea/workflows/ over the
GitHub-convention .github/ equivalents. Moves all issue templates and
workflow files to the Gitea-native paths and updates CLAUDE.md references.
Cosign certificate identity paths in release/rollback workflows are
intentionally left unchanged — they reference the signing identity from
prior workflow runs and will need a separate update when the CI signing
infrastructure migrates.
Co-Authored-By: Paperclip <noreply@paperclip.ing>