feat(config): moderate spawn tuning for Alex's Mobs, Fowl Play, Critters

Every visible entity multiplies the client render cost (vanilla, EMF/FA,
GeckoLib, ETF, dynamic lights) and the server tick. These cuts target only the
species that are heavy by weight x group size. Rare mobs keep their defaults.

- Alex's Mobs: halve 9 common weights (gazelle and capuchin herds, straddler,
  rocky roller, underminer, elephant, blobfish, mudskipper, caiman).
- Fowl Play: lower duck/goose/gull/sparrow weights and max group sizes
  (upstream #214, ~400 ducks on rivers, is still open in 1.2.3).
- Critters and Companions: about 40% off sea bunnies and the forest/lush bug
  rules. It does have a spawn config; configVersion 2 skips its v1->v2
  migration.

All three are partial files. NeoForge (TOML) and YACL 3.8.2 (JSON5) keep
defaults for missing keys. Shipped enforced from config/ because the server
reads them from this repo. Details and the B14 measurement plan:
analysis/client-perf/SPAWN-TUNING.md.

.packwizignore

@@ -65,3 +65,8 @@ config/paxi/datapacks/*
 # Default Options copies them into place client-side, only when the target is absent.
 !config/defaultoptions
 !config/defaultoptions/**
+# Server spawn tuning (analysis/client-perf/SPAWN-TUNING.md); partial files, the mods
+# fill in defaults for every other key. Enforced: the server reads them from here.
+!config/alexsmobs-common.toml
+!config/fowlplay.json5
+!config/crittersandcompanions-common.json5