chore: configure codecov checks as informational (#654)

## Summary

- Add patch coverage target at 50%
- Set both project and patch status checks to informational mode so they
report coverage but never block CI

Co-authored-by: Claude Opus 4.6 <[email protected]>

Author: vdusek

codecov.yaml

@@ -4,3 +4,8 @@ coverage:
       default:
         target: auto
         threshold: 0.10%   # tolerate up to 0.10% decrease
+        informational: true # CI check reports status but never fails
+    patch:
+      default:
+        target: 50%         # error only if patch coverage drops below 50%
+        informational: true  # CI check reports status but never fails