gitignore: scope overrides ignore to mods/, track defaultconfigs/

The previous rule 'pack/overrides/' ignored the whole directory, which
made it impossible to re-include subpaths via ! exception (git's rule).

Narrow the ignore to 'pack/overrides/mods/' -- the only path that
Build-Tweaks.ps1 actually writes -- and drop the broken whitelist
block. Other subdirs under pack/overrides/ (defaultconfigs/, etc.) now
live in git like normal source.

Adds the Waystones override that 0.16.1 attempted (spawnInVillages =
DISABLED). Bumps to 0.16.3 so launcher caches re-sync.

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": "0.16.2",
+  "version": "0.16.3",
   "minecraft": "1.21.1",
   "loader": {
     "type": "neoforge",