feat(api): add price history, Stringee SMS, Zalo OA, WebSocket notifications, and feature-listing command

- Add PriceHistory model + migration, price-changed domain event, and event handler
- Add GetPriceHistory query handler and controller endpoint
- Implement StringeeSmsService and ZaloOaService with unit tests
- Add Zalo ZNS templates for Vietnamese notification messages
- Add WebSocket notification gateway for real-time push
- Add FeatureListingCommand for promoted listings
- Apply remaining consistent-type-imports lint fixes across API modules

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

apps/api/src/modules/notifications/infrastructure/services/zalo-oa.service.ts

@@ -0,0 +1,149 @@
+import { Injectable, type OnModuleInit } from '@nestjs/common';
+import { type LoggerService } from '@modules/shared';
+
+export interface SendZaloOaDto {
+  /** Zalo user ID (follower UID from OA) */
+  toUid: string;
+  /** ZNS template ID registered in Zalo OA Manager */
+  templateId: string;
+  /** Template parameter key-value pairs */
+  templateData: Record<string, string>;
+}
+
+export interface ZaloOaMessageResult {
+  messageId: string;
+}
+
+const MAX_RETRIES = 3;
+const BASE_DELAY_MS = 1000;
+
+/**
+ * Service for sending template-based messages via Zalo Official Account (OA) API v3.
+ *
+ * Uses the Zalo Notification Service (ZNS) to deliver transactional messages
+ * such as new inquiry alerts, payment confirmations, and listing status changes.
+ *
+ * Requires ZALO_OA_ACCESS_TOKEN and ZALO_OA_ID to be configured.
+ */
+@Injectable()
+export class ZaloOaService implements OnModuleInit {
+  private oaId = '';
+  private accessToken = '';
+  private initialized = false;
+  private readonly znsUrl = 'https://business.openapi.zalo.me/message/template';
+
+  constructor(private readonly logger: LoggerService) {}
+
+  onModuleInit(): void {
+    this.oaId = process.env['ZALO_OA_ID'] ?? '';
+    this.accessToken = process.env['ZALO_OA_ACCESS_TOKEN'] ?? '';
+
+    if (!this.oaId || !this.accessToken) {
+      this.logger.warn(
+        'ZALO_OA_ID or ZALO_OA_ACCESS_TOKEN not set — Zalo OA notifications disabled',
+        'ZaloOaService',
+      );
+      return;
+    }
+
+    this.initialized = true;
+    this.logger.log(
+      `Zalo OA configured for OA ID "${this.oaId}"`,
+      'ZaloOaService',
+    );
+  }
+
+  get isAvailable(): boolean {
+    return this.initialized;
+  }
+
+  /**
+   * Send a template-based message to a Zalo user via ZNS (Zalo Notification Service).
+   *
+   * The user must be a follower of the Official Account, and the template must be
+   * pre-registered and approved in the Zalo OA Manager console.
+   */
+  async sendMessage(dto: SendZaloOaDto): Promise<ZaloOaMessageResult> {
+    return this.sendWithRetry(dto);
+  }
+
+  private async sendWithRetry(dto: SendZaloOaDto): Promise<ZaloOaMessageResult> {
+    if (!this.initialized) {
+      throw new Error('Zalo OA not initialized — ZALO_OA_ID / ZALO_OA_ACCESS_TOKEN not configured');
+    }
+
+    let lastError: Error | undefined;
+
+    for (let attempt = 1; attempt <= MAX_RETRIES; attempt++) {
+      try {
+        const result = await this.send(dto);
+        return result;
+      } catch (error) {
+        lastError = error instanceof Error ? error : new Error(String(error));
+
+        if (attempt < MAX_RETRIES) {
+          const delayMs = BASE_DELAY_MS * Math.pow(2, attempt - 1);
+          this.logger.warn(
+            `Zalo OA attempt ${attempt}/${MAX_RETRIES} failed: ${lastError.message}. Retrying in ${delayMs}ms...`,
+            'ZaloOaService',
+          );
+          await this.delay(delayMs);
+        }
+      }
+    }
+
+    this.logger.error(
+      `Zalo OA message failed after ${MAX_RETRIES} attempts: ${lastError?.message}`,
+      'ZaloOaService',
+    );
+    throw lastError;
+  }
+
+  private async send(dto: SendZaloOaDto): Promise<ZaloOaMessageResult> {
+    const body = {
+      phone: dto.toUid,
+      template_id: dto.templateId,
+      template_data: dto.templateData,
+    };
+
+    const response = await fetch(this.znsUrl, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        access_token: this.accessToken,
+      },
+      body: JSON.stringify(body),
+    });
+
+    if (!response.ok) {
+      const errorText = await response.text().catch(() => 'Unknown error');
+      throw new Error(`Zalo OA API error (${response.status}): ${errorText}`);
+    }
+
+    const data = (await response.json()) as {
+      error?: number;
+      message?: string;
+      data?: { msg_id?: string };
+    };
+
+    // Zalo API returns error=0 on success
+    if (data.error !== undefined && data.error !== 0) {
+      throw new Error(
+        `Zalo OA message rejected (code ${data.error}): ${data.message ?? 'Unknown reason'}`,
+      );
+    }
+
+    const messageId = data.data?.msg_id ?? `zalo-oa-${Date.now()}`;
+
+    this.logger.log(
+      `Zalo OA message sent to ${dto.toUid.slice(0, 6)}***: ${messageId}`,
+      'ZaloOaService',
+    );
+
+    return { messageId };
+  }
+
+  private delay(ms: number): Promise<void> {
+    return new Promise((resolve) => setTimeout(resolve, ms));
+  }
+}