feat(pack): ship offline usernamecache to clients for Jade

Jade resolves tamed-animal owner names client-side; its Mojang profile
lookup can't resolve offline-mode UUIDs and it falls back to NeoForge's
UsernameCache, which the client loads from <game>/usernamecache.json.
Ship that file (side = "client", installed at the game root) so migrated
owners stop showing as "???".

Maintain the mapping with tools/sync-usernamecache.py after new logins.

pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "f9852076c38404288e9f09588cdae45b6e3a51fb8333099953566abbe06c791a"
+hash = "65215ee765ac7e8321c232dd2624f7453aed4900384a18b004410d77158f7b6d"
 
 [versions]
 minecraft = "1.21.1"