feat(pack): add QoL/JEI mod set as packwiz external files

Nine NeoForge 1.21.1 jars hosted under pack/custom/ with hand-written
mods/*.pw.toml (JEI + JER + JEProfessions, Jade + JadeAddons, Balm,
InventoryEssentials, MouseTweaks, CustomSkinLoader). Adds
CustomSkinLoader.json config; refreshes index.toml/pack.toml.

Jars are committed because external files have no upstream URL — the
pack/custom/ copy served by caddy is the source of truth.

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

pack/pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "7b81c9e9d9e6e21a9865a2dded0dfd77e7683d679b98fe5b0114eaed9a31f17e"
+hash = "64c69b2e38fcf389a3de38d240aa95e8309ac60e717c1fe994aef2c4a2684921"
 
 [versions]
 minecraft = "1.21.1"