Fixes#6438
When a protected branch requires signed commits and no signing key is available, fast-forward-only merges should still be allowed because they do not create a new commit.
This patch applies signing checks by merge behaviour/style instead of one global gate:
- pass `mergeStyle` through `CheckPullMergeable(...)` in web/API/automerge paths
- require signing for commit-creating styles (`merge`, `rebase`, `rebase-merge`, `squash`)
- bypass signing precheck only for `fast-forward-only`
- align merge UI options with backend behaviour so signing-dependent styles are unavailable when signing cannot happen
- add Go unit tests for merge-style signing requirements
- add frontend unit coverage for the no-allowed-merge-styles guard
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11403
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: abdo <dev@abdo.wtf>
Co-committed-by: abdo <dev@abdo.wtf>
- Don't double escape the 'Delete branch "$BRANCH"' text. `Locale.Tr`
escapes the argument already and Vue does too by default.
- Let Vue escape the text and add a unit test ensuring that it escapes.
- Resolves#5582
