Build-Pack: default tweak jars to side=server, 0.22.2 -> 0.22.3

URGENT client-side fix. brassandsigil_tweaks-1.0.0.jar (built from
pack/tweaks/ into pack/overrides/mods/) declares lithostitched as a
hard dependency in its mods.toml. lithostitched is tagged side=server
in the lockfile because it's worldgen-only. brassandsigil_tweaks had
no explicit side tag so Build-Pack defaulted it to side=both. Clients
downloaded the tweak jar but not the dep -> NeoForge refused to start
with 'Mod brassandsigil_tweaks requires lithostitched 1.7 or above'.

Fix: Build-Pack now injects side='server' on any local-override file
under mods/. All tweak jars are data-only (worldgen modifiers, recipe
overrides) and pure server-side. If a future tweak is actually client-
relevant, this rule will need a per-file exception.

Tested in build output -- the brassandsigil_tweaks entry now shows
side='server' in the generated manifest.

pack/pack.lock.json

@@ -1,7 +1,7 @@
 {
   "$schema": "Brass-and-Sigil pack.lock.json - generated, do not edit by hand unless you know what you are doing",
   "name": "Brass and Sigil",
-  "version": "0.22.2",
+  "version": "0.22.3",
   "minecraft": "1.21.1",
   "loader": {
     "type": "neoforge",