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.

pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "07463f2d8920a7a3ec3f9b3d7d5f0883ed265d3bc8c34e0c956b09d8ce277814"
+hash = "f4b8ec15830662e033bd5c7723357a58aeeaf9dad1c5957f103961fb83ee0fd1"
 
 [versions]
 minecraft = "1.21.1"