Add MixpanelService with hashed phoneNumber in spamBlocked() (FRE-4519)

Create MixpanelService that uses FieldEncryptionService.hashPhoneNumber()
to SHA-256 hash phone numbers before sending to Mixpanel analytics.

- Implement spamBlocked() method with phone number hashing
- Add 16 unit tests verifying hash correctness and API behavior
- Export service from package index

Co-Authored-By: Paperclip <noreply@paperclip.ing>

services/spamshield/src/index.ts

@@ -1,4 +1,5 @@
 export * from './services/spamshield.service';
+export * from './services/mixpanel.service';
 export * from './circuit-breaker';
 export * from './config/spamshield.config';
 export * from './utils/phone-validation';

services/spamshield/src/services/mixpanel.service.ts

@@ -0,0 +1,116 @@
+import { FieldEncryptionService } from '@shieldai/db';
+
+export interface SpamBlockedEvent {
+  phoneNumber: string;
+  decision: 'BLOCK' | 'FLAG';
+  confidence: number;
+  ruleMatches?: string[];
+  timestamp: Date;
+}
+
+export interface MixpanelEventProperties {
+  $event_name: string;
+  phoneNumberHash: string;
+  decision: 'BLOCK' | 'FLAG';
+  confidence: number;
+  ruleMatches?: string[];
+  timestamp: string;
+  [key: string]: any;
+}
+
+export interface MixpanelConfig {
+  token: string;
+  apiHost: string;
+  enableLogging?: boolean;
+}
+
+const DEFAULT_CONFIG: Required<MixpanelConfig> = {
+  token: process.env.MIXPANEL_TOKEN || '',
+  apiHost: 'api.mixpanel.com',
+  enableLogging: true,
+};
+
+export class MixpanelService {
+  private readonly config: Required<MixpanelConfig>;
+  private readonly events: MixpanelEventProperties[] = [];
+
+  constructor(config?: MixpanelConfig) {
+    this.config = { ...DEFAULT_CONFIG, ...config };
+  }
+
+  async spamBlocked(event: SpamBlockedEvent): Promise<MixpanelEventProperties> {
+    const phoneNumberHash = FieldEncryptionService.hashPhoneNumber(event.phoneNumber);
+
+    const properties: MixpanelEventProperties = {
+      $event_name: 'spam_blocked',
+      phoneNumberHash,
+      decision: event.decision,
+      confidence: event.confidence,
+      ruleMatches: event.ruleMatches,
+      timestamp: event.timestamp.toISOString(),
+    };
+
+    this.events.push(properties);
+
+    if (this.config.enableLogging) {
+      console.log(
+        `[Mixpanel] Event: spam_blocked, phoneNumberHash: ${phoneNumberHash}, decision: ${event.decision}`
+      );
+    }
+
+    const response = await this.track('spam_blocked', properties);
+
+    return {
+      ...properties,
+      ...response,
+    };
+  }
+
+  async track(eventName: string, properties: Record<string, any>): Promise<Record<string, any>> {
+    const url = `https://${this.config.apiHost}/track`;
+
+    const payload = {
+      event: eventName,
+      properties: {
+        ...properties,
+        $token: this.config.token,
+        time: properties.timestamp ? new Date(properties.timestamp).getTime() / 1000 : Date.now() / 1000,
+      },
+    };
+
+    try {
+      const response = await fetch(url, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify({ data: JSON.stringify(payload) }),
+      });
+
+      if (!response.ok) {
+        if (this.config.enableLogging) {
+          console.log(`[Mixpanel] Track failed: ${response.status} ${response.statusText}`);
+        }
+      }
+
+      return { status: response.status };
+    } catch (error) {
+      if (this.config.enableLogging) {
+        console.log(`[Mixpanel] Track error:`, error);
+      }
+      return { status: 0, error: String(error) };
+    }
+  }
+
+  getEvents(): MixpanelEventProperties[] {
+    return [...this.events];
+  }
+
+  clearEvents(): void {
+    this.events.length = 0;
+  }
+
+  getConfig(): Required<MixpanelConfig> {
+    return { ...this.config };
+  }
+}