Minor cleanups: gitignore out/, expect() messages, comment wording

- .gitignore: ignore the /out/ ISO build dir
- bos-settings: use expect() with messages over unwrap() for piped stdio;
  drop a stray blank line
- pacman.conf: reword the SigLevel=Never TODO as a future-improvement note

iso/airootfs/etc/pacman.conf

@@ -35,7 +35,8 @@ Include = /etc/pacman.d/mirrorlist
 #
 # Forgejo signs the repo db with a key pacman can't look up, so TrustAll
 # fails. SigLevel = Never skips verification (acceptable for this private
-# repo over TLS). TODO: import Forgejo's signing key + SigLevel = Required.
+# repo over TLS). Future improvement: import Forgejo's signing key and
+# switch to SigLevel = Required for full package verification.
 # -----------------------------------------------------------------------
 # The section name must match Forgejo's served db filename
 # ({owner}.{group}.{domain}.db) — pacman fetches "<section>.db" from Server.