fix(audiobookshelf): set the port with the env names the image actually reads

The first deploy of the unit failed its own health gate in the worst possible shape:
systemd said active (running), the engine logged a clean database init, and the
server then listened on :80 under base path /audiobookshelf - so every probe of
:8000 was refused and wait_for_health timed out at 180s beside a container that
looked healthy.

Cause: ABS_PORT / ABS_CONFIG_DIR / ABS_METADATA_DIR / ABS_PUID are the npm
package's names, printed by the server README; this image never reads them. Its own
contract, read off the pinned digest with podman inspect, is PORT=80
CONFIG_PATH=/config METADATA_PATH=/metadata, and the server greps for exactly PORT,
CONFIG_PATH, METADATA_PATH, ROUTER_BASE_PATH. The two path variables appeared to
work only because the image already exports the same values - the coincidence that
made the inert lines look correct.

The unit now speaks the image's names, adds ROUTER_BASE_PATH=/ so the service is
the plain host:port the docs and the homepage card promise, and the dead ABS_*
lines are deleted instead of kept as decoration. Proven against the same digest in
a throwaway container (temp state dirs, loopback-only mapping, removed after):
base path "/", listening on :8000, GET /healthcheck -> 200, and the old prefixed
path -> 404.

Guards: the quadlet seam now refuses an Environment=ABS_* line and requires
PORT/ROUTER_BASE_PATH; the vault page gains the law with its failure signature and
the two-second image-inspect check. Suite: ALL TESTS PASSED, 812 ok.

serverAppConfigs-docs/Dankserver/Audiobookshelf.md

@@ -25,7 +25,8 @@ manager) — **Internal-only:** LAN address, no vhost, no DNS name.
 |------|-------|
 | Unit file | `dankserver/audiobookshelf/quadlet/audiobookshelf.container` (the authority for every number here) |
 | Image | `ghcr.io/advplyr/audiobookshelf` pinned by **amd64 manifest digest** — see Laws |
-| Port | `PublishPort=8000:8000` — web UI and API on the same port |
+| Port | `Environment=PORT=8000` + `PublishPort=8000:8000` — web UI and API on one port |
+| Base path | `Environment=ROUTER_BASE_PATH=/` — the URL is the plain `host:port`, no `/audiobookshelf` prefix |
 | Network | `pasta` (standalone; publishes nothing to other containers) |
 | Audio bind | `/mnt/entropy/Audiobooks:/audiobooks:ro` — read-only, by design |
 | State | `/home/dank/Containers/audiobookshelf/config` → `/config`, `…/metadata` → `/metadata` (both NVMe) |
@@ -52,6 +53,14 @@ browser and lives in the `config` bind on the SSD.
 
 ## Laws
 
+- **Speak the image's env names, not the README's.** The server reads `PORT`,
+  `CONFIG_PATH`, `METADATA_PATH` and `ROUTER_BASE_PATH`; the `ABS_*` family printed
+  by the server's own README is the npm package's naming and is **inert** in this
+  image. Measured 2026-11-02 on the first deploy: with `ABS_PORT=8000` the server
+  listened on `:80` under base path `/audiobookshelf`, so `systemctl` said
+  `active (running)` while every probe of `:8000` was refused and the deploy gate
+  failed at 180 s. Two seconds with the pinned digest settles it:
+  `podman inspect --format '{{.Config.Env}}' <image>`.
 - **The audio bind stays `:ro`.** ABS writes nothing that belongs beside the
   audio: its library, covers, progress and sidecar metadata all land in
   `/metadata` on the SSD. A writable bind would put stray writes on the spindle