fix(aria): convert all PostgreSQL named enum columns to VARCHAR

All named enum types (threat_severity, attack_phase, event_type, ioc_type,
ioc_source, confidence_level, sequence_type, auto_response_action,
os_eol_status) have been converted to VARCHAR via V3 migration. Hibernate
@Enumerated(EnumType.STRING) binds values as character varying which
PostgreSQL rejects without explicit casts on both INSERT and SELECT.

Reverts the native @Query workarounds added in the previous two commits —
simple derived query methods now work correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/com/hiveops/aria/controller/DevicePostureController.java

@@ -52,7 +52,7 @@ public class DevicePostureController {
         Pageable pageable = PageRequest.of(page, size);
 
         if (osEolStatus != null) {
-            return postureRepository.findByOsEolStatusNativeOrderByPostureScoreAsc(osEolStatus.name(), pageable);
+            return postureRepository.findByOsEolStatusOrderByPostureScoreAsc(osEolStatus, pageable);
         }
         if ("low".equals(scoreFilter)) {
             return postureRepository.findByPostureScoreLessThanOrderByPostureScoreAsc(50, pageable);