ci: add ready_for_review trigger to PR validation workflow (#36)

When a draft PR is converted to ready-for-review, the ready_for_review
event fires but the workflow was not configured to listen for it. This
caused PR validation checks to remain in a skipped state permanently.

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

Author: GoogilyBoogily

.github/workflows/enforce-conventional-pr-title.yml

@@ -8,6 +8,7 @@ on:
       - reopened
       - synchronize
       - labeled
+      - ready_for_review
 
 jobs:
   pr-title-check: