chore(mods): classify owo-lib as both

Dependency library declaring side=BOTH; keep server-side so any
server-loaded dependent doesn't crash on a missing lib.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CAvxmMjspjDw7Fkkmy86EN

mods-sides.json

@@ -151,6 +151,7 @@
   "moonlight-neoforge-1.21.1-3.0.22.jar": "both",
   "morefunctionalstorage-1.2.3.jar": "both",
   "moreoverlays-1.24.2-mc1.21.1-neoforge.jar": "client",
+  "owo-lib-neoforge-0.12.15.5-beta.1+1.21.jar": "both",
   "polymorph-neoforge-1.1.0+1.21.1.jar": "both",
   "ponderjs-neoforge-1.21.1-2.4.0.jar": "client",
   "rechiseled-1.2.5-neoforge-mc1.21.jar": "both",