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/gcsStorage.ts

@@ -958,7 +958,7 @@ export class GcsStorage extends BaseStorage {
     useCache?: boolean
   }): Promise<{
     nodes: HNSWNode[]
-    totalCount?: number
+    totalCount: number
     hasMore: boolean
     nextCursor?: string
   }> {
@@ -1029,6 +1029,7 @@ export class GcsStorage extends BaseStorage {
 
           return {
             nodes,
+            totalCount: this.totalNounCount,
             hasMore: !!nextCursor,
             nextCursor
           }
@@ -1038,6 +1039,7 @@ export class GcsStorage extends BaseStorage {
         if (response?.nextPageToken) {
           return {
             nodes,
+            totalCount: this.totalNounCount,
             hasMore: true,
             nextCursor: `${shardIndex}:${response.nextPageToken}`
           }
@@ -1049,6 +1051,7 @@ export class GcsStorage extends BaseStorage {
       // No more shards or nodes
       return {
         nodes,
+        totalCount: this.totalNounCount,
         hasMore: false,
         nextCursor: undefined
       }
@@ -1220,6 +1223,7 @@ export class GcsStorage extends BaseStorage {
 
       return {
         items: filteredVerbs,
+        totalCount: this.totalVerbCount,
         hasMore: !!response?.nextPageToken,
         nextCursor: response?.nextPageToken
       }