feat: WhatsApp AI assistant — provider-agnostic messaging with Gupshup

Provider-agnostic WhatsApp integration for AI-driven appointment booking:

- MessagingProvider interface (sendText, sendButtons, sendList, parseInbound)
- GupshupProvider implementation (Gupshup WhatsApp API)
- MessagingService — AI orchestration with tools (department/doctor/slot
  lists via interactive WhatsApp messages, appointment booking, caller
  resolution + context injection)
- Redis conversation history (24h TTL, matches WhatsApp session window)
- Webhook controller at POST /api/messaging/webhook

Swappable to Ozonetel or Meta Cloud API by implementing MessagingProvider
and switching MESSAGING_PROVIDER env var.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/messaging/messaging-conversation.service.ts

@@ -0,0 +1,41 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import Redis from 'ioredis';
+import { ConversationEntry } from './types';
+
+@Injectable()
+export class MessagingConversationService {
+    private readonly logger = new Logger(MessagingConversationService.name);
+    private readonly redis: Redis;
+    private readonly ttlSec = 24 * 60 * 60; // 24h — matches WhatsApp session window
+    private readonly maxHistory = 20;
+
+    constructor(config: ConfigService) {
+        const redisUrl = config.get<string>('redis.url') ?? 'redis://localhost:6379';
+        this.redis = new Redis(redisUrl);
+    }
+
+    private key(phone: string): string {
+        return `wa:conv:${phone}`;
+    }
+
+    async getHistory(phone: string): Promise<ConversationEntry[]> {
+        const raw = await this.redis.get(this.key(phone));
+        if (!raw) return [];
+        try {
+            return JSON.parse(raw);
+        } catch {
+            return [];
+        }
+    }
+
+    async addMessages(phone: string, entries: ConversationEntry[]): Promise<void> {
+        const existing = await this.getHistory(phone);
+        const updated = [...existing, ...entries].slice(-this.maxHistory);
+        await this.redis.setex(this.key(phone), this.ttlSec, JSON.stringify(updated));
+    }
+
+    async clear(phone: string): Promise<void> {
+        await this.redis.del(this.key(phone));
+    }
+}