v2: fail (exit 1) on naming violation

The four wired repos flip the naming job to a required status check
(agenthub#557 WS6); a check that always exits 0 can never gate. v2 makes
the script exit nonzero with FAIL lines; warn-only stays available via
job-level continue-on-error or the legacy @v1 tag. dfritz break-glass
exemption unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

action.yaml

@@ -1,8 +1,9 @@
 name: Check branch/PR naming
 description: |
   Validates that a PR's head branch and title follow the fritzlab naming
-  standard. Always exits 0 — warn-only until the Bugs system is live.
-  Produces WARN log lines for any violation.
+  standard. Fails (exits 1) on any violation, with FAIL log lines naming
+  it. Warn-only wiring is the consumer's choice: set
+  continue-on-error: true on the job (or pin @v1, which never fails).
 
   Standard:
     branch:   <role>/bug-<id>/<kebab>   e.g. dev/bug-x7k2m9/fix-terminal-resize