fix: improve AI Assist input visibility and use valid Qwen models

- Added text-slate-100 dark:text-slate-100 to input for visible text on dark bg
- Updated Qwen models to use valid names: qwen-coder-plus, qwen-turbo, etc
- Set qwen-coder-plus as default model for best coding assistance

lib/services/qwen-oauth.ts

@@ -1116,7 +1116,11 @@ Perform analysis based on provided instructions.`,
 
   getAvailableModels(): string[] {
     return [
-      "coder-model",
+      "qwen-coder-plus",
+      "qwen-plus",
+      "qwen-turbo",
+      "qwen-max",
+      "qwen-coder-turbo",
     ];
   }
 }