[TASK] Implement drop old versions endpoint

Description

Implement DELETE /v1/maintenance/_oldVersions in MaintenanceResource.java. Deletes all versions of versionable objects (Contentlets, Containers, Templates, Links, Workflow History) older than a specified date.

Acceptance Criteria

• API caller must provide a date query parameter in MM/dd/yyyy format
• Endpoint must call CMSMaintenanceFactory.deleteOldAssetVersions(date)
• API caller must receive the count of deleted records in response
• API caller must receive a success indicator (deletedCount >= 0 means success, -1 means error)
• Must require CMS Administrator role and Maintenance portlet access
• API caller must receive 400 Bad Request if date is missing or invalid

Priority

None

Additional Context

• CMSMaintenanceFactory.deleteOldAssetVersions() iterates in 30-day chunks from the oldest inode date to the specified date, each chunk in a Hibernate transaction
• Deletes via: DropOldContentletRunner (contentlets), ContainerAPI.deleteOldVersions(), TemplateAPI.deleteOldVersions(), MenuLinkAPI.deleteOldVersions(), WorkflowAPI.deleteWorkflowHistoryOldVersions()
• Flushes all caches when totalRecords > 0
• Can take minutes on large datasets
• DWR legacy: CMSMaintenanceAjax.removeOldVersions(date) line 260

Start in MaintenanceResource.java and compare the requested endpoint with the legacy CMSMaintenanceAjax.removeOldVersions(date) at line 260. Trace CMSMaintenanceFactory.deleteOldAssetVersions(date) and the existing maintenance authorization patterns. Done means the DELETE endpoint validates MM/dd/yyyy input, enforces the required access, returns the deletion count and success indicator, and responds with 400 for missing or invalid dates.