Validate active job pagination parameters

[codingkiddo]

Context

The activeJobOverview endpoint accepts optional startingIndex and pageSize query parameters.

Previously, these values were converted directly using Integer.parseInt. Invalid values such as negative integers, non-numeric strings, empty values, or values exceeding the integer range could either be passed to the resource-cluster layer or result in an internal server error.

This change validates both pagination parameters before invoking the underlying service.

Invalid values now return 400 Bad Request with a clear error message:

• startingIndex must be a non-negative integer
• pageSize must be a non-negative integer

The change also preserves pageSize=0 as a valid value.

Changes

• Added validation for startingIndex and pageSize.
• Rejected negative, non-numeric, empty, and overflowing integer values.
• Added clear client-facing validation messages.
• Added tests covering invalid pagination parameters.
• Added a regression test for a negative startingIndex.
• Added coverage confirming that pageSize=0 remains valid.
• Verified that invalid requests do not reach the resource-cluster layer.

Checklist

• ./gradlew build compiles code correctly
• Added new tests where applicable
• ./gradlew test passes all tests
• Extended README or added javadocs where applicable

README and Javadoc changes are not applicable because this change only validates existing API parameters and does not introduce a new public API.