feat: add comprehensive per-service statistics tracking

Add full support for tracking and analyzing data by service in multi-tenant deployments.

## Features Added

- **Service Statistics Tracking**: Track nouns, verbs, and metadata counts per service
- **Service Activity Monitoring**: Track first/last activity timestamps and operation counts
- **New API Methods**:
  - `listServices()`: List all services with their statistics and status
  - `getServiceStatistics(service)`: Get detailed stats for a specific service
  - Enhanced `getStatistics()` with service filtering and breakdown

- **Service Filtering**: Filter search results and queries by service
- **Storage Enhancements**: BaseStorageAdapter tracks service activity with timestamps
- **Type Definitions**: Added ServiceStatistics interface and extended StatisticsData

## Implementation Details

- Services automatically tracked via defaultService config or per-operation override
- Service status detection (active/inactive/read-only) based on activity
- Memory-efficient tracking at statistics level, not per noun/verb
- Backward compatible - existing data tracked under 'default' service

## Documentation

- Comprehensive guide in docs/guides/per-service-statistics.md
- Examples for multi-tenant apps, health monitoring, and auditing
- API reference and migration guide included

## Testing

- Full test suite in tests/service-statistics.test.ts
- Coverage of all new methods and filtering capabilities

This enables better observability, debugging, and management of multi-service Brainy deployments, addressing the need to track individual service performance when multiple services share storage.

src/storage/adapters/baseStorageAdapter.ts

@@ -138,7 +138,17 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
       verbCount: { ...statistics.verbCount },
       metadataCount: { ...statistics.metadataCount },
       hnswIndexSize: statistics.hnswIndexSize,
-      lastUpdated: statistics.lastUpdated
+      lastUpdated: statistics.lastUpdated,
+      // Include serviceActivity if present
+      ...(statistics.serviceActivity && {
+        serviceActivity: Object.fromEntries(
+          Object.entries(statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+        )
+      }),
+      // Include services if present
+      ...(statistics.services && {
+        services: statistics.services.map(s => ({...s}))
+      })
     }
 
     // Schedule a batch update instead of saving immediately
@@ -263,7 +273,17 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
         verbCount: { ...statistics.verbCount },
         metadataCount: { ...statistics.metadataCount },
         hnswIndexSize: statistics.hnswIndexSize,
-        lastUpdated: statistics.lastUpdated
+        lastUpdated: statistics.lastUpdated,
+        // Include serviceActivity if present
+        ...(statistics.serviceActivity && {
+          serviceActivity: Object.fromEntries(
+            Object.entries(statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+          )
+        }),
+        // Include services if present
+        ...(statistics.services && {
+          services: statistics.services.map(s => ({...s}))
+        })
       }
     }
 
@@ -277,6 +297,9 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
     const counter = counterMap[type]
     counter[service] = (counter[service] || 0) + amount
 
+    // Track service activity
+    this.trackServiceActivity(service, 'add')
+
     // Update timestamp
     this.statisticsCache!.lastUpdated = new Date().toISOString()
 
@@ -284,6 +307,41 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
     this.scheduleBatchUpdate()
   }
 
+  /**
+   * Track service activity (first/last activity, operation counts)
+   * @param service The service name
+   * @param operation The operation type
+   */
+  protected trackServiceActivity(
+    service: string,
+    operation: 'add' | 'update' | 'delete'
+  ): void {
+    if (!this.statisticsCache) {
+      return
+    }
+
+    // Initialize serviceActivity if it doesn't exist
+    if (!this.statisticsCache.serviceActivity) {
+      this.statisticsCache.serviceActivity = {}
+    }
+
+    const now = new Date().toISOString()
+    const activity = this.statisticsCache.serviceActivity[service]
+
+    if (!activity) {
+      // First activity for this service
+      this.statisticsCache.serviceActivity[service] = {
+        firstActivity: now,
+        lastActivity: now,
+        totalOperations: 1
+      }
+    } else {
+      // Update existing activity
+      activity.lastActivity = now
+      activity.totalOperations++
+    }
+  }
+
   /**
    * Decrement a statistic counter
    * @param type The type of statistic to decrement ('noun', 'verb', 'metadata')
@@ -309,7 +367,17 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
         verbCount: { ...statistics.verbCount },
         metadataCount: { ...statistics.metadataCount },
         hnswIndexSize: statistics.hnswIndexSize,
-        lastUpdated: statistics.lastUpdated
+        lastUpdated: statistics.lastUpdated,
+        // Include serviceActivity if present
+        ...(statistics.serviceActivity && {
+          serviceActivity: Object.fromEntries(
+            Object.entries(statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+          )
+        }),
+        // Include services if present
+        ...(statistics.services && {
+          services: statistics.services.map(s => ({...s}))
+        })
       }
     }
 
@@ -323,6 +391,9 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
     const counter = counterMap[type]
     counter[service] = Math.max(0, (counter[service] || 0) - amount)
 
+    // Track service activity
+    this.trackServiceActivity(service, 'delete')
+
     // Update timestamp
     this.statisticsCache!.lastUpdated = new Date().toISOString()
 
@@ -349,7 +420,17 @@ export abstract class BaseStorageAdapter implements StorageAdapter {
         verbCount: { ...statistics.verbCount },
         metadataCount: { ...statistics.metadataCount },
         hnswIndexSize: statistics.hnswIndexSize,
-        lastUpdated: statistics.lastUpdated
+        lastUpdated: statistics.lastUpdated,
+        // Include serviceActivity if present
+        ...(statistics.serviceActivity && {
+          serviceActivity: Object.fromEntries(
+            Object.entries(statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+          )
+        }),
+        // Include services if present
+        ...(statistics.services && {
+          services: statistics.services.map(s => ({...s}))
+        })
       }
     }
 

src/storage/adapters/memoryStorage.ts

@@ -622,6 +622,16 @@ export class MemoryStorage extends BaseStorage {
       metadataCount: {...statistics.metadataCount},
       hnswIndexSize: statistics.hnswIndexSize,
       lastUpdated: statistics.lastUpdated,
+      // Include serviceActivity if present
+      ...(statistics.serviceActivity && {
+        serviceActivity: Object.fromEntries(
+          Object.entries(statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+        )
+      }),
+      // Include services if present
+      ...(statistics.services && {
+        services: statistics.services.map(s => ({...s}))
+      }),
       // Include distributedConfig if present
       ...(statistics.distributedConfig && { 
         distributedConfig: JSON.parse(JSON.stringify(statistics.distributedConfig)) 
@@ -648,6 +658,16 @@ export class MemoryStorage extends BaseStorage {
       metadataCount: {...this.statistics.metadataCount},
       hnswIndexSize: this.statistics.hnswIndexSize,
       lastUpdated: this.statistics.lastUpdated,
+      // Include serviceActivity if present
+      ...(this.statistics.serviceActivity && {
+        serviceActivity: Object.fromEntries(
+          Object.entries(this.statistics.serviceActivity).map(([k, v]) => [k, {...v}])
+        )
+      }),
+      // Include services if present
+      ...(this.statistics.services && {
+        services: this.statistics.services.map(s => ({...s}))
+      }),
       // Include distributedConfig if present
       ...(this.statistics.distributedConfig && { 
         distributedConfig: JSON.parse(JSON.stringify(this.statistics.distributedConfig))