[Studio] fix: validate audit query and cleanup parameters

[btlqql]

Summary

• validate audit query pagination before reading repository data
• use long arithmetic for pagination bounds to avoid integer overflow
• reject zero or negative audit cleanup retention values
• add regression tests for invalid and extreme inputs

Problem and root cause

AuditService.queryLogs used unchecked int values directly in subList index calculations. Non-positive inputs could produce invalid indices, and multiplying large positive page values could overflow. cleanupLogs similarly accepted non-positive retention periods, allowing a cutoff at the current time or in the future and risking deletion of recent audit entries.

Impact

Invalid requests now fail predictably with BusinessException code 400 before repository work begins. Valid large pagination inputs no longer overflow, and cleanup always requires a positive retention period.

Verification

• mvn -o -B -ntp -Dtest=AuditServiceTest test — 16 tests passed
• mvn -o -B -ntp test — 161 tests passed
• Checkstyle — 0 violations
• git diff --cached --check — passed

Fixes #441