feat(audiobookshelf): the audiobook server as a boot-persistent quadlet

Audiobookshelf serves /mnt/entropy/Audiobooks to browsers and phones with its own
library and per-listener positions. The design point of the unit: every byte this
server writes is its own state - SQLite library, accounts, progress, cached covers
- and all of it lands on the NVMe under /home/dank/Containers/audiobookshelf. The
audio bind is :ro, so a stray sidecar write onto the spindle is structurally
impossible rather than merely discouraged, and the array keeps exactly one
sanctioned write path (scripts/media-view.sh).

Three failure modes the unit is shaped around:

- Bind-source ordering. In a rootless unit RequiresMountsFor= is inert and
  ConditionPathIsMountPoint= is fail-dead, so a missing array does not stop the
  start: podman invents an empty directory and the first scan records an empty
  library as truth. ExecStartPre=wait-for-mount.sh is the gate that works here,
  the same one copyparty uses.
- The health binary. The image is Alpine: wget, no curl. A curl HealthCmd reads a
  healthy server as unhealthy and Restart=always turns that into a loop.
- The image pin. podman records the linux/amd64 manifest for what it pulled, not
  the manifest-list digest `latest` points at, so the amd64 digest is the pin that
  names the build this host runs. Upstream version tags stop at 2.19.0 while
  `latest` is newer, so latest@digest is the only form that is both current and
  exact - the jellyfin/romm precedent.

The first-boot scan reads the whole tree once, so IOWeight=10 keeps it behind
playback; that weight is only honoured because the user.slice accounting drop-in
and the user@1000 delegation are installed by the deployer.

Deployer registration is the standard four touch-points (client gate, remote
allowlist + handler + dispatcher, planner order/set/path map, test routing). The
handler creates both state roots before the first start - letting podman invent
them leaves the SQLite file unwritable by the container user under a rootless
first boot - and gates on /healthcheck.

dankserver/audiobookshelf/quadlet/audiobookshelf.container

@@ -0,0 +1,59 @@
+# Quadlet unit: Audiobookshelf audiobook server (rootless, boot-persistent).
+#
+# Install path on dankserver: ~/.config/containers/systemd/audiobookshelf.container
+# Unit name: audiobookshelf.service (podman 5.x drops the container- prefix)
+#
+# Everything this server writes is its own state — the SQLite library, accounts,
+# playback progress, cached covers — and it lives under
+# /home/dank/Containers/audiobookshelf on the NVMe, so no metadata byte ever
+# lands on the spindle. The audio itself is bound READ-ONLY off the array: the
+# only sanctioned write path into /mnt/entropy is the overlay view
+# (scripts/media-view.sh), Audiobookshelf has no need of it, and a read-only bind
+# makes a stray sidecar write structurally impossible rather than discouraged.
+#
+# The digest is the linux/amd64 manifest of the tag, which is what podman
+# verifies and what RepoDigests records on this single-arch host. Pinning the
+# manifest-list digest instead would let a re-pull resolve to a different image.
+# The upstream version tags stop at 2.19.0 (built 2025-02-02) while `latest` is
+# newer by a year and a half, so `latest@digest` is the only pin that names the
+# build actually running — same reasoning as the jellyfin and romm units.
+
+[Unit]
+Description=Audiobookshelf audiobook server container
+After=network.target
+
+[Container]
+ContainerName=audiobookshelf
+Image=ghcr.io/advplyr/audiobookshelf:latest@sha256:37c2057e150694970442579815c646fe6bdc01c95b9d1547c4c9068be8844ef3
+Network=pasta
+Environment=ABS_CONFIG_DIR=/config
+Environment=ABS_METADATA_DIR=/metadata
+Environment=ABS_PGID=1000
+Environment=ABS_PORT=8000
+Environment=ABS_PUID=1000
+Environment=TZ=America/Vancouver
+PublishPort=8000:8000
+Volume=/home/dank/Containers/audiobookshelf/config:/config
+Volume=/home/dank/Containers/audiobookshelf/metadata:/metadata
+Volume=/mnt/entropy/Audiobooks:/audiobooks:ro
+# The image is Alpine: it ships wget and no curl, so the health check must name
+# the binary that exists or the container is unhealthy while serving perfectly.
+HealthCmd=wget -q -O /dev/null http://127.0.0.1:8000/healthcheck
+HealthInterval=30s
+HealthTimeout=10s
+HealthRetries=3
+
+[Service]
+# Refuse to start until the array is a real mount — with the bind source missing,
+# podman invents an empty directory and Audiobookshelf records an empty library as
+# truth. See the header of scripts/wait-for-mount.sh for the blind-boot incident.
+ExecStartPre=/home/dank/serverAppConfigs/scripts/wait-for-mount.sh /mnt/entropy
+Restart=always
+RestartSec=5
+# The first boot scans the whole audiobook tree. Weighted LOW (default 100) so a
+# scan loses to playback when the array is contended. Proportional share, not a
+# cap: inert while the disk is idle.
+IOWeight=10
+
+[Install]
+WantedBy=default.target