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>

docker-compose.yml

@@ -47,7 +47,7 @@ services:
       context: ./backend
       dockerfile: Dockerfile
       args:
-        CACHEBUST: "9"
+        CACHEBUST: "10"
     restart: unless-stopped
     environment:
       # ── Core ─────────────────────────────────────────────