Fix: Switch Vision core to black-forest-labs/FLUX.1-schnell for superior image generation

backend/controllers/ai.js

@@ -21,7 +21,7 @@ const MODELS = {
   'Codex Fero': 'moonshotai/Kimi-K2-Thinking',
   'Codex Zenith': 'Qwen/Qwen3-Coder-480B-A35B-Instruct',
   'Codex Magna': 'moonshotai/Kimi-K2.5',
-  'Codex Vision': 'zai-org/GLM-Image'
+  'Codex Vision': 'black-forest-labs/FLUX.1-schnell'
 };
 
 const PROVIDERS = {};