ops: docker prune timer, kanboard backup/healthcheck, backup script fixes

docker-maintenance/ adds a systemd timer + prune.sh for the root LV that holds
Docker's data-root and has filled to 100% before, risking ENOSPC corruption.
The script sticks to the safe reclaim set (builder cache, dangling images,
stopped containers) and deliberately avoids `-a` and volume pruning, which can
destroy live data when run unattended.

kanboard/backup.sh and healthcheck.sh bring Kanboard in line with the other
services. seafile/ and vaultwarden/ backup scripts get fixes carried from the
stability audit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docker-maintenance/README.md

@@ -0,0 +1,108 @@
+# Docker Maintenance — Growth Guard (kb#184)
+
+## Background
+
+2026-07-24: root LV (`/`, holds Docker's data-root) filled to 1.5G free / 100% used —
+risk of ENOSPC corruption across every service on Agap. Emergency reclaim (builder
+prune + dangling images + stopped containers) took it to 25G free / 90% used.
+
+2026-07-26 (this task): re-measured before any action — still 24G free / 90% used
+(the emergency fix hadn't regrown, but hadn't been made recurring either). Ran
+`prune.sh` live: root went to **40G free / 83% used**. Breakdown before/after:
+
+| | Before | After |
+|---|---|---|
+| Images (total/reclaimable) | 88GB / 62.41GB (70%) | 87.2GB / 62.41GB (71%) |
+| Build Cache (total/reclaimable) | 18.74GB / 14.49GB | 4.25GB / 0B |
+| Root free | 24G (90% used) | 40G (83% used) |
+
+The 62.41GB of image "reclaimable" space barely moved — that's almost entirely
+**tagged-but-unused** images (`docker image prune -a` territory), not dangling ones.
+See the decision below.
+
+## What `prune.sh` does (safe scope only)
+
+```
+docker builder prune -f      # build cache — always safe, fully rebuildable
+docker container prune -f    # stopped/exited containers only
+docker image prune -f        # DANGLING images only (untagged) — no -a
+```
+
+Logs before/after `docker system df` to `prune.log`, and pushes the post-prune
+build-cache-reclaimable size (bytes) to Zabbix host `AgapHost` (hostid 10776),
+trapper item `docker.buildcache.reclaimable.bytes` (itemid 70624, **type 2 —
+confirmed to accept `history.push` on this Zabbix instance, unlike the type-2
+"Calculated" items other tasks found dead; verified live 2026-07-26**).
+
+Test without changing anything:
+```bash
+bash /home/alvis/agap_git/docker-maintenance/prune.sh --dry-run
+```
+
+## Explicitly NOT automated (human decision required)
+
+- **`docker image prune -a`** — would reclaim ~62GB of tagged-but-currently-unused
+  images (e.g. `cognee/cognee-mcp:1.2.2` at 17.9GB, `cognee` variants, old
+  `ghcr.io/open-webui/open-webui`, `lscr.io/linuxserver/calibre`/`zotero` at
+  3.5GB each — many belong to services that are stopped/replaced but the image
+  may still be wanted for a quick restart). **Decision recorded, not made**:
+  someone with knowledge of which of these services are truly retired should
+  either (a) run `docker image prune -a` manually after reviewing the image
+  list (`docker system df -v`), or (b) curate a keep-list and prune around it.
+  Not scheduled — this script will never run `-a`.
+- **`docker volume prune`** — never automated; can destroy live data for a
+  volume that's temporarily unmounted. Not touched by this script or its guard.
+
+## Zabbix
+
+- Item: `docker.buildcache.reclaimable.bytes` on host `AgapHost` (hostid 10776,
+  itemid 70624), type Trapper, units B. Pushed once per `prune.sh` run (post-prune
+  value — after a scheduled run this should almost always read near 0).
+- Trigger (triggerid 32970): fires if `last()` of that item exceeds 20GB
+  (21474836480 bytes) — i.e. the build cache grew back past the safe threshold
+  between scheduled runs, meaning the timer isn't running or needs to run more
+  often.
+- Zabbix runs on **lizacer** (`http://192.168.1.4:81`), not Agap.
+
+## Scheduled run — NOT INSTALLED (handoff required)
+
+This directory contains the tested script only. Installing the schedule is a
+human step (per Agap automation policy: no unattended agent installs a cron/
+timer that acts on a live target). To install:
+
+**Cron** (matches the existing `agap_git/kanboard` pattern — user crontab, no sudo):
+```bash
+crontab -e
+# add:
+0 4 * * * /home/alvis/agap_git/docker-maintenance/prune.sh >> /home/alvis/agap_git/docker-maintenance/prune.log 2>&1
+```
+Runs daily at 04:00. Adjust frequency if build-cache growth between runs proves
+faster than expected (watch the Zabbix trigger above).
+
+Alternative — **systemd user timer**, unit files provided in this directory
+(`docker-prune.service`, `docker-prune.timer`), not installed:
+```bash
+mkdir -p ~/.config/systemd/user
+cp /home/alvis/agap_git/docker-maintenance/docker-prune.service ~/.config/systemd/user/
+cp /home/alvis/agap_git/docker-maintenance/docker-prune.timer ~/.config/systemd/user/
+systemctl --user daemon-reload
+systemctl --user enable --now docker-prune.timer
+```
+
+Either mechanism is fine; cron matches existing Agap convention (kanboard
+healthcheck/backup) so it's the recommended default.
+
+## Acceptance status (kb#184)
+
+- [x] Immediate reclaim (2026-07-24, prior task) — done.
+- [x] Recurring prune script — written, tested (dry-run + live run confirmed
+      it reclaims builder cache + dangling images safely).
+- [ ] **Schedule installed** — script + cron line + systemd unit files are ready;
+      installing them is a human step (see above). **Handoff: run the `crontab -e`
+      command above, or install the systemd timer.**
+- [x] Build-cache Zabbix trigger — created (triggerid 32970), verified
+      `history.push` lands (item read back 14490000000 during test, then 0
+      after the live prune run).
+- [x] `docker image prune -a` decision — recorded above as an open human
+      decision, not automated.
+- [x] df / free space — 40G free (83% used) as of 2026-07-26, up from 24G/90%.