feat: appointment QR code — generated and sent via WhatsApp after booking

- QrService: generates QR PNG from appointment data, cached in-memory
- GET /api/messaging/qr/:appointmentId serves the image (Gupshup needs URL)
- sendImage added to MessagingProvider + GupshupProvider
- send_appointment_qr tool registered in ToolRegistry
- Flow JSON updated: QR sent after booking confirmation
- Variable interpolation now supports dot notation ({{result.field}})
- SIDECAR_PUBLIC_URL env var for the QR image URL

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

src/messaging/messaging.controller.ts

@@ -1,6 +1,8 @@
-import { Controller, Post, Body, Logger } from '@nestjs/common';
+import { Controller, Post, Get, Body, Param, Res, Logger } from '@nestjs/common';
+import type { Response } from 'express';
 import { MessagingProvider } from './providers/messaging-provider.interface';
 import { MessagingService } from './messaging.service';
+import { QrService } from './qr.service';
 
 @Controller('api/messaging')
 export class MessagingController {
@@ -9,6 +11,7 @@ export class MessagingController {
     constructor(
         private readonly provider: MessagingProvider,
         private readonly messaging: MessagingService,
+        private readonly qr: QrService,
     ) {}
 
     @Post('webhook')
@@ -33,4 +36,17 @@ export class MessagingController {
 
         return { status: 'ok' };
     }
+
+    // Serve QR code images — Gupshup needs a public URL to send images
+    @Get('qr/:appointmentId')
+    async serveQr(@Param('appointmentId') appointmentId: string, @Res() res: Response) {
+        const png = this.qr.get(appointmentId);
+        if (!png) {
+            res.status(404).json({ error: 'QR code not found or expired' });
+            return;
+        }
+        res.set('Content-Type', 'image/png');
+        res.set('Cache-Control', 'public, max-age=86400');
+        res.send(png);
+    }
 }