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/deploy-remote.sh

@@ -1318,6 +1318,12 @@ deploy_audiobookshelf() {
     # /healthcheck answers once the HTTP server is bound; the library scan that
     # follows runs in the background and must not gate the deploy.
     wait_for_health audiobookshelf http://127.0.0.1:8000/healthcheck 90
+    # A server with no root user and no library is "healthy" and useless, so the
+    # bootstrapper runs after the health gate and its failure fails the deploy:
+    # it creates the account (credential in the mode-600 host secret file), the
+    # Audiobooks library over the /audiobooks bind, and fires the scan. Every
+    # step is idempotent, so a re-deploy costs one incremental scan.
+    scripts/audiobookshelf-init.sh
 }
 
 # The content server's single admin account and the desktop's basic-auth