fix: widen rents.usd_amount column, add webhook alias, silence cron spam

- Migration to ALTER rents.usd_amount from numeric(5,2) to numeric(15,2)
  which was causing "numeric field overflow" 500 errors when saving
  rental prices >= 1000 sats (e.g. 1200 sats)
- Also widen season_rents.usd_amount for consistency
- Add /webhooks/btcpay route alias (BTCPay was posting to /btcpay but
  the endpoint was /btcpay-webhook, causing 404s on payment callbacks)
- Skip ECS autoscaling cron when TRANSCODING_API_URL is not set
  (eliminates "security token invalid" error spam every minute)
- Reduce payment cron from EVERY_MINUTE to EVERY_10_MINUTES to avoid
  429 rate limiting on the BTC price API
- Bump API CACHEBUST to 10

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/transcoding-server/transcoding-server.service.ts

@@ -102,10 +102,12 @@ export class TranscodingServerService {
     Logger.log(`Auto Scaling group scaled to ${desiredCount} instances`);
   }
 
-  // Run the autoscaling logic every hour
+  // Run the autoscaling logic every hour (AWS ECS only).
+  // Skip when using the local FFmpeg worker (no TRANSCODING_API_URL).
   @Cron(CronExpression.EVERY_MINUTE)
   async autoscaleEcsService() {
     if (process.env.ENVIRONMENT !== 'production') return;
+    if (!process.env.TRANSCODING_API_URL) return;
     try {
       const queueSize = await this.getQueueSize();
       const currentTaskCount = await this.describeService(