fix: add PR merge conflict check to dev agent workflow

Dev agent should check if PR has merge conflicts before asking for review.
This prevents approving a PR that has conflicts, which could introduce
new errors after rebase.

Changes:
- Add conflict check step in workflow for both with/without user message cases
- Use mergeable field from PR API to detect conflicts
- Instructions to rebase and resolve conflicts if mergeable: false

skills/kugetsu/scripts/kugetsu-session.sh

@@ -341,8 +341,6 @@ Tools for PR interaction:
 - Post issue/PR comment: curl -X POST "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN" -H "Content-Type: application/json" -d '{"body":"Your comment"}'
 - List PR comments: curl -s "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN"
 - List PR reviews: curl -s "https://$instance/api/v1/repos/$owner/$repo/pulls/$number/reviews" -H "Authorization: Bearer \$GITEA_TOKEN"
-  - IMPORTANT: After listing reviews, READ the review comments and incorporate feedback
-  - Check for review state: "APPROVED" means ready to merge, "COMMENT" means feedback to address
 - Merge PR (only with approval): tea pr merge --repo $owner/$repo $number --style merge
   - MERGING requires approval first! Check for: approval in reviews, OR "lgtm"/"approved" in comments
   - If no approval, ask reviewer to approve first before merging