fix: litestream healthcheck gate + 1yr retention

Re-enable deploy gate on litestream: pgrep-based healthcheck with 6
retries (30s window) after a 15s start period — broken backups now
fail the deploy loudly instead of silently succeeding.

Extend retention from 7d to 1yr (8760h): WAL frames are tiny for a
low-traffic app, R2 free tier covers years of storage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

padelnomics/litestream.yml

@@ -17,5 +17,5 @@ dbs:
         access-key-id: ${LITESTREAM_R2_ACCESS_KEY_ID}
         secret-access-key: ${LITESTREAM_R2_SECRET_ACCESS_KEY}
         endpoint: https://${LITESTREAM_R2_ENDPOINT}
-        retention: 168h
+        retention: 8760h
         snapshot-interval: 6h