feat(providers): add System One (Jev) decision endpoint

New /v1/systemone pass-through route for Jev decision models (jev-1.13,
jev-1.13-free) on OpenCode Zen and the free lane. Follows the media-route
pattern: systemoneConfig in the registry drives URL/headers, the handler
mirrors the embeddings account-fallback + usage flow, and the dashboard
gains a System One media-provider kind. No chat-pipeline changes.

Co-Authored-By: Claude Code <noreply@anthropic.com>

open-sse/providers/index.js

@@ -23,7 +23,7 @@ function buildTransport(transport, oauth) {
 const MEDIA_KEYS = new Set([
   "serviceKinds", "ttsConfig", "sttConfig", "embeddingConfig",
   "imageConfig", "imageToTextConfig", "videoConfig", "musicConfig",
-  "searchViaChat", "searchConfig", "fetchConfig",
+  "searchViaChat", "searchConfig", "fetchConfig", "systemoneConfig",
   "modelsFetcher", "mediaPriority", "hiddenKinds",
 ]);