feat: landing zone backup to R2 via rclone + Litestream

Landing files (append-only JSON.gz) synced to R2 every 30 min via
systemd timer + rclone. Extraction state DB (.state.sqlite) continuously
replicated via Litestream (second DB entry). Auto-restore on container
startup for both app.db and .state.sqlite. Reuses existing R2 bucket
and credentials — no new env vars needed.

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

infra/landing-backup/padelnomics-landing-backup.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Sync landing zone to R2 every 30 minutes
+
+[Timer]
+OnBootSec=5min
+OnUnitActiveSec=30min
+
+[Install]
+WantedBy=timers.target