fix: PREFER_AMD_GPU now lives in globals so config API changes affect GPU routing

Previously gpu_router.py had its own module-level PREFER_AMD_GPU constant
that was frozen at import time. The config API wrote to globals.PREFER_AMD_GPU
which didn't exist, so runtime GPU preference changes never took effect.

Now globals.py owns PREFER_AMD_GPU and gpu_router reads it from there.

bot/utils/gpu_router.py

@@ -37,7 +37,8 @@ MODEL_TO_GPU = {
 }
 
 # Configuration
-PREFER_AMD_GPU = os.getenv("PREFER_AMD_GPU", "false").lower() == "true"
+# PREFER_AMD_GPU lives in globals so the config API can update it at runtime.
+# We read globals.PREFER_AMD_GPU in functions below instead of a frozen local.
 AMD_MODELS_ENABLED = os.getenv("AMD_MODELS_ENABLED", "true").lower() == "true"
 
 
@@ -101,7 +102,7 @@ def get_llama_url_with_load_balancing(
             return globals.LLAMA_URL, "llama3.1"
     
     # AMD enabled - implement load balancing
-    use_amd = prefer_amd or PREFER_AMD_GPU or (random.random() < 0.5)
+    use_amd = prefer_amd or globals.PREFER_AMD_GPU or (random.random() < 0.5)
     
     if task_type == "evil":
         # Evil/uncensored models