Refactor to local-first architecture on Hetzner NVMe

Remove distributed R2/Iceberg/SSH pipeline architecture in favor of
local subprocess execution with NVMe storage. Landing data backed up
to R2 via rclone timer.

- Strip Iceberg catalog, httpfs, boto3, paramiko, prefect, pyarrow
- Pipelines run via subprocess.run() with bounded timeouts
- Extract writes to {LANDING_DIR}/psd/{year}/{month}/{etag}.csv.gzip
- SQLMesh reads LANDING_DIR variable, writes to DUCKDB_PATH
- Delete unused provider stubs (ovh, scaleway, oracle)
- Add rclone systemd timer for R2 backup every 6h
- Update supervisor to run pipelines with env vars

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

infra/backup/materia-backup.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=Materia Landing Data Backup to R2
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/rclone sync /data/materia/landing/ r2:materia-raw/landing/ --log-level INFO
+TimeoutStartSec=1800