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.

dankserver/audiobookshelf/quadlet/audiobookshelf.container

@@ -26,11 +26,18 @@ After=network.target
 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
+# The names are the image's own: the server reads PORT, CONFIG_PATH, METADATA_PATH
+# and ROUTER_BASE_PATH (measured against the digest below — `podman inspect` shows
+# PORT=80 CONFIG_PATH=/config METADATA_PATH=/metadata in the image ENV, and the
+# server's source greps for exactly these). The ABS_* family printed by the server
+# README is the npm package's naming and is INERT here: with ABS_PORT=8000 the
+# server listened on :80 under base path /audiobookshelf, so the unit sat
+# `active (running)` while every probe to :8000 was refused (measured 2026-11-02,
+# first deploy). ROUTER_BASE_PATH=/ is what makes the URL the plain host:port.
+Environment=PORT=8000
+Environment=ROUTER_BASE_PATH=/
+Environment=CONFIG_PATH=/config
+Environment=METADATA_PATH=/metadata
 Environment=TZ=America/Vancouver
 PublishPort=8000:8000
 Volume=/home/dank/Containers/audiobookshelf/config:/config