feat(forgejo-backup): migrate to pg_dump -> restic -> Hetzner S3 (DEV-514)
Replaces the legacy volume-based backup that wrote pg_dump files to
`platform-backup-data` (RWO PVC on hcloud volume 106575948). That
volume was deleted externally on 2026-08-17; instead of re-provisioning
the legacy pattern, this migrates forgejo to the restic->S3 pipeline
already in use for loki/grafana/prometheus (DEV-485..DEV-492).
- initContainer runs pg_dump -F c into emptyDir (5 GiB cap)
- main container: restic backup /source, tag forgejo, repo
s3:${S3_ENDPOINT}/${S3_BUCKET}/restic/forgejo
- forget/prune (7d/4w/6m), check --read-data-subset=5%
- textfile-collector metrics -> backup_forgejo.prom (DEV-494 wiring)
- SealedSecret forgejo-s3-backup mirrors monitoring-s3-backup fields
- retire platform-backup-data PVC manifest
Verified manually 2026-08-23 01:11 UTC:
forgejo-backup-manual-1787447497 -> snapshot a961a473, repo 192 KiB.
Orphan PV/PVC (`platform-backup-data`, `pvc-de59ae9c-...`) deleted.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
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