fix(opencode): route Muse Spark models to Responses API and declare vision

Route all Muse Spark models (not just 1.2) on OpenCode Free to
/zen/v1/responses via isMuseSparkModel(), fixing HTTP 500 on
muse-spark-1.3-contributor-free. Declare vision:true on Muse Spark
models so image input is no longer stripped; register 1.3 in the
registry and capabilities. Scoped to opencode only — other providers
keep Chat Completions routing.

open-sse/providers/models/helpers.js

@@ -18,3 +18,10 @@ export function withCodexReviewModels(models) {
     ];
   });
 }
+
+export function isMuseSparkModel(modelId) {
+  if (!modelId || typeof modelId !== "string") return false;
+  const clean = modelId.replace(/\([^()]+\)\s*$/, "").trim();
+  const base = clean.includes("/") ? clean.split("/").pop() : clean;
+  return /^muse[-_]?spark(?:$|[-_:.\s])/i.test(base);
+}