feat(opencode-go): add muse-spark-1.3-contributor and fix parallel tool calls on Responses paths (#3819)

- Add muse-spark-1.3-contributor as responses-only model on OpenCode Go with dedicated executor
- Key Responses→chat streaming tool calls by item_id to prevent parallel tool calls merging into index 0
- Standardize tool coercions and call_id clamping in Responses API translation

tests/unit/opencode-go-models.test.js

@@ -27,6 +27,7 @@ describe("OpenCode Go model catalog", () => {
       "mimo-v2.5", "mimo-v2.5-pro",
       "minimax-m3", "minimax-m2.7", "minimax-m2.5",
       "qwen3.7-max", "qwen3.7-plus", "qwen3.6-plus",
+      "muse-spark-1.3-contributor",
     ]);
   });
 });