fix: extend OrgStructureCache TTL and add graceful shutdown cleanup

- Extended OrgStructureCache TTL from 10 to 30 minutes (reduce cleanup frequency)
- Added orgStructureCache.destroy() in graceful shutdown handler
- Updated documentation to reflect changes

Co-Authored-By: Claude (glm-4.7) <noreply@anthropic.com>

src/utils/OrgStructureCache.ts

@@ -5,7 +5,7 @@ interface CacheEntry {
 
 class OrgStructureCache {
   private cache: Map<string, CacheEntry> = new Map();
-  private readonly CACHE_TTL = 10 * 60 * 1000; // 10 minutes
+  private readonly CACHE_TTL = 30 * 60 * 1000; // 30 minutes
   private isInitialized = false;
   private cleanupTimer: NodeJS.Timeout | null = null;
 
@@ -17,7 +17,7 @@ class OrgStructureCache {
     if (this.isInitialized) return;
 
     this.isInitialized = true;
-    // Cleanup expired entries every 10 minutes
+    // Cleanup expired entries every 30 minutes
     this.cleanupTimer = setInterval(() => {
       this.cleanup();
     }, this.CACHE_TTL);