feat(perf): add one-step tier setup script for existing players

Default Options only seeds configs when absent, so existing players never
got the tuned settings. build.py --ship now also writes the Deck/Mid/High
tier files to config/onion-perf/<tier>/, and onion-perf-setup.{sh,ps1,bat}
(installed into the instance folder) backs up and replaces the tier's
config files and merges only the tuned video keys into options.txt,
keeping keybinds, audio and vsync/max-FPS choices.

PLAYER-TUNING: point players at the script; bench B4 GC verdict (G1 for
everyone; ZGC/Shenandoah tested worse); 16 GB PCs 5-6 GB heap.

.packwizignore

@@ -69,3 +69,12 @@ config/paxi/datapacks/*
 # ModernFix mixin overrides (build.py SHIP; enforced - ModernFix reads it before
 # Default Options runs). dynamic_resources=true per bench B6.
 !config/modernfix-mixins.properties
+# Player tier overrides (build.py --ship) plus the per-machine setup script that
+# applies a tier to an existing install (see PLAYER-TUNING.md §1). Must come after
+# the blanket config/* and *.json patterns above (last matching pattern wins), and
+# the directory itself must be re-included before anything under it.
+!config/onion-perf
+!config/onion-perf/**
+!onion-perf-setup.sh
+!onion-perf-setup.ps1
+!onion-perf-setup.bat