[FEATURE] Cache Management APIs

Problem

Cache management (flushing caches, viewing region names, viewing cache statistics) is currently only accessible via JSP. The cache region dropdown is populated by a JSP scriptlet calling CacheLocator.getCacheIndexes(). Cache statistics (JVM memory + per-provider per-region hit/miss rates) are rendered by cachestats_guava.jsp. Flushing a specific cache region uses a Struts form POST to ViewCMSMaintenanceAction._flush(). Need REST endpoints to answer "What's in cache and how do I flush it?"

Goal

Provide REST endpoints for listing cache region names, viewing cache statistics, and flushing cache regions with proper side effects (permission reset, PushPublishing filter reload).

APIs

• GET /v1/caches — List cache region names for selection
• GET /v1/caches/stats — Cache statistics with JVM memory and per-region hit/miss rates
• DELETE /v1/caches/{regionName} — Flush specific region or all caches

Personas

• Developer Teams — Need REST APIs for Angular Cache tab
• System Administrators — Need to monitor cache health and flush caches when troubleshooting

Legacy Reference

• JSP: view_cms_maintenance.jsp lines 1327–1427 (Cache tab)
• JSP: cachestats_guava.jsp (cache stats rendering)
• Struts Action: ViewCMSMaintenanceAction._flush() lines 273–280
• Target Class: CacheResource.java (/api/v1/caches)

Start with CacheResource.java at /api/v1/caches, then compare the cache behavior in view_cms_maintenance.jsp, cachestats_guava.jsp, and ViewCMSMaintenanceAction._flush(). Implement the three listed endpoints for region names, JVM and per-region statistics, and flushing, including the stated permission reset and PushPublishing filter reload side effects. Done means the REST APIs support the Angular Cache tab and administrator troubleshooting needs.