refactor(pack): host custom jars from ./custom outside the pack root

Move pack/custom/ -> ./custom/ and bind-mount it into caddy at
/srv/pack/custom (served URL pack.${BASE_DOMAIN}/custom/ unchanged).
Keeping jars outside the packwiz pack root stops `packwiz refresh`
from indexing them as direct files on top of the mods/*.pw.toml
external refs (drops 9 bogus custom/*.jar entries from index.toml).

add-custom-mod.sh now writes jars to ./custom/. Trim the blessingskin
caddy override to just the conf swap (volumes merge by target).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tooling/add-custom-mod.sh

@@ -6,8 +6,9 @@
 # <slug>.pw.toml that points at a stable download URL + sha256, then refresh.
 #
 # Since the jars are local (no public URL), we HOST them on the caddy pack
-# server: each jar is copied under pack/custom/ — caddy serves pack/ at
-# http://pack.${BASE_DOMAIN}/ — so the metadata's download url is
+# server: each jar is copied to the top-level ./custom/ dir (OUTSIDE ./pack, so
+# packwiz refresh won't index it as a direct file). Caddy bind-mounts ./custom
+# at /srv/pack/custom, so it is served at
 #   http://pack.${BASE_DOMAIN}/custom/<filename>
 # which is exactly what minecraft fetches via PACKWIZ_URL on install.
 #
@@ -73,7 +74,7 @@ else
   JARS=("$TARGET")
 fi
 
-mkdir -p pack/custom pack/mods
+mkdir -p custom pack/mods
 
 # ---- per-jar processing (no refresh; refresh once at the end) --------------
 add_one() {  # $1 = jar path. Uses NAME (single-jar only), SIDE, FORCE, BASE_DOMAIN.
@@ -88,7 +89,7 @@ add_one() {  # $1 = jar path. Uses NAME (single-jar only), SIDE, FORCE, BASE_DOM
   [ -n "$slug" ] || die "could not derive a slug from name '$name'"
 
   meta="pack/mods/${slug}.pw.toml"
-  dest="pack/custom/${filename}"
+  dest="custom/${filename}"
   url="http://pack.${BASE_DOMAIN}/custom/${filename}"
 
   if [ "$FORCE" -ne 1 ]; then
@@ -119,4 +120,4 @@ for j in "${JARS[@]}"; do add_one "$j"; done
 # .pw.toml files are picked up. Must run inside the pack dir.
 ( cd pack && packwiz refresh )
 log "packwiz refresh done — ${#JARS[@]} mod(s) added to the pack"
-echo "  commit pack/custom/*.jar, pack/mods/*.pw.toml, pack/index.toml, pack/pack.toml"
+echo "  commit custom/*.jar, pack/mods/*.pw.toml, pack/index.toml, pack/pack.toml"