fix(storage): resolve persistence restart bug across all storage adapters

Critical bug fix that restores data persistence after application restart for all storage adapters (GCS, S3, OPFS, FileSystem).

**Root Cause:**
Storage adapters were loading entity counts from _system/counts.json but not returning totalCount in pagination methods, causing rebuildIndexesIfNeeded() to see undefined and incorrectly assume no data existed.

**Changes:**
- GCS Storage: Return totalCount in getNodesWithPagination() and getVerbsWithPagination()
- S3 Storage: Call initializeCounts() in init() and return totalCount in pagination methods
- OPFS Storage: Call initializeCounts() in init() to load pre-calculated counts
- BaseStorage: Add defensive validation to prevent future adapters from missing totalCount

**Impact:**
- Production deployments now work correctly (Cloud Run, AWS, Kubernetes)
- Data persists correctly across container restarts
- Serverless scale-to-zero deployments now functional
- All storage adapters use O(1) pre-calculated counts (scales to millions of entities)

**Testing:**
- Build passes with no TypeScript errors
- All existing tests pass
- Defensive validation ensures future storage adapters won't have this bug

Fixes critical production issue affecting all persistent storage deployments.

src/storage/adapters/opfsStorage.ts

@@ -132,6 +132,9 @@ export class OPFSStorage extends BaseStorage {
         create: true
       })
 
+      // Initialize counts from storage
+      await this.initializeCounts()
+
       this.isInitialized = true
     } catch (error) {
       console.error('Failed to initialize OPFS storage:', error)