feat(audiobookshelf): bootstrap the account, library and scan from the deployer

A freshly deployed Audiobookshelf answers /healthcheck and is otherwise dead: no
account, no library, no scan. The UI registration step is gone by design — the
doors are POST /init (200 with plain text "OK", not JSON) and /status (isInit),
and there is no /setup route. That is an API-only bootstrap, so it must be code.

scripts/audiobookshelf-init.sh is idempotent: /status -> /init when unregistered,
POST /login for the bearer, POST /api/libraries for the Audiobooks library on
/audiobooks, then POST /api/libraries/{id}/scan. The deployer runs it only after
the health gate has answered.

Credentials live in ~/.config/secrets/audiobookshelf (mode 600): the bearer rides
an Authorization header and the password only a POST body — never a URL or argv,
where any ps on the host would print them. The seam drives an inline stub server
that logs every request line, and asserts: fresh bootstrap creates account,
library and scan; a second run creates nothing new and still fires the
incremental scan; no secret appears in any logged request line; a server that
refuses is reported as "refused: <url>" with exit 1 rather than success; ABS_SCAN
outside 0|1 fails before a single request; the deployer orders init after health.

Measured on Dankserver: run against the already-bootstrapped host it is a no-op
that re-fires the scan; the library then scans (1,500+ books, every item with
audio tracks, none invalid).

scripts/test-changed.sh

@@ -104,6 +104,12 @@ for path in "${CHANGED[@]}"; do
         dankserver/jellyfin/quadlet/*|dankserver/plex/quadlet/*)
             add_test tests/media_overlay.bats
             ;;
+        # The Audiobookshelf bootstrapper (account + library + scan over the API)
+        # and the deployer hook that runs it after the health gate.
+        scripts/audiobookshelf-init.sh|tests/audiobookshelf_init.bats)
+            add_test tests/audiobookshelf_init.bats
+            add_test tests/deployment_flow.bats
+            ;;
         shared/homepage/*)
             add_test tests/homepage_caddy.bats
             add_test tests/homepage_config.bats