Add remote offload of completed backups to Hetzner Storage Box

Ships every completed backup off-box over WebDAV via rclone, verified by
exact byte-size match before local retention or schedule rotation ever
touches it. Fixes prune_orphans to skip confirmed-offloaded backups whose
local copy was already purged (it previously hard-deleted their DB row,
discarding the only pointer to the remote copy). Installs rclone in the
Docker image and gitignores the container's rclone.conf location, which
lives inside the bind-mounted repo root and holds live credentials.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XjW4qocnaJxhugUi5ca8Wo

CLAUDE.md

@@ -146,7 +146,7 @@ Nested `CLAUDE.md` files (loaded automatically by Claude Code only when a file i
 | `devplacepy/services/moderation/CLAUDE.md` | Trust and safety: the reportable-target registry, the content filter and its five choke points, the report queue and its atomic resolution, enforcement, consent, maturity, account deletion |
 | `devplacepy/services/acceptance/CLAUDE.md` | Acceptance convergence: the opt-in service that grants every policy agreement to every account that has not declined it, its invisibility contract and the ledger-as-decline-register rule |
 | `devplacepy/services/audit/CLAUDE.md` | Audit log: recorders, categories, retention |
-| `devplacepy/services/backup/CLAUDE.md` | Backup service: targets, worker, schedules, primary-admin-only download |
+| `devplacepy/services/backup/CLAUDE.md` | Backup service: targets, worker, schedules, primary-admin-only download, remote offload to Hetzner Storage Box |
 | `devplacepy/services/telegram/CLAUDE.md` | Telegram bot bridge |
 | `devplacepy/services/email/CLAUDE.md` | Devii IMAP/SMTP email tools |
 | `devplacepy/services/gitea/CLAUDE.md` | Issue tracker (Gitea-backed, no local issue store) |