feat(opencode): add --pure flag and model variant config

src/opencodeService.ts

@@ -60,8 +60,11 @@ Generate a concise Conventional Commit message for these changes:`;
     return new Promise((resolve, reject) => {
         const args: string[] = [
             "run",
+            "--pure",
             "--format",
             "default",
+            "-m",
+            "opencode/gpt-5-nano",
             "--variant",
             "minimal",
         ];