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/CustomSkinLoader/CustomSkinLoader.json

@@ -0,0 +1,12 @@
+{
+    "enable": true,
+    "loadlist": [
+        {
+            "name": "Ulicraft Skins",
+            "type": "MojangAPI",
+            "apiRoot": "https://auth.ulicraft.lan/account/",
+            "sessionRoot": "https://auth.ulicraft.lan/session/"
+        }
+    ]
+}
+