docs: add CodeRabbit auto-summary integration to PR template

Integrates CodeRabbit's automatic summary generation feature into the pull request template by adding a trigger command and informational comment.

This enables automated PR summaries when CodeRabbit is enabled, streamlining the review process and reducing manual effort in documenting changes.

.github/pull_request_template.md

@@ -10,10 +10,13 @@
 ## 🔖 Summary
 <!--
 A concise description of the changes introduced by this PR.
+CodeRabbit will auto-generate a summary here if enabled.
 Example:
-“Add real-time currency conversion widget to dashboard.”
+"Add real-time currency conversion widget to dashboard."
 -->
 
+@coderabbitai summary
+
 ## 🏷️ Ticket / Issue
 <!--
 Link to the related ticket, issue or user story.