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.

tests/dankserver_quadlet.bats

@@ -175,3 +175,15 @@ load helpers
     printf '%s\n' "$body" | grep -q 'audiobookshelf/metadata' || return 1
     printf '%s\n' "$body" | grep -q 'wait_for_health audiobookshelf' || return 1
 }
+
+@test "audiobookshelf sets its port and base path with the names the image reads" {
+    # Measured 2026-11-02 on the first deploy: ABS_PORT / ABS_CONFIG_DIR are the npm
+    # package's names and this image ignores them, so the server came up on :80
+    # under base path /audiobookshelf and the deploy gate timed out beside a unit
+    # that was active (running). PORT and ROUTER_BASE_PATH are what the image's own
+    # ENV block and the server source actually use.
+    unit="$REPO_ROOT/dankserver/audiobookshelf/quadlet/audiobookshelf.container"
+    grep -q '^Environment=PORT=8000$' "$unit" || return 1
+    grep -q '^Environment=ROUTER_BASE_PATH=/$' "$unit" || return 1
+    ! grep -qE '^Environment=ABS_' "$unit" || return 1
+}