fix: proper VRAM cleanup on model unload + CUDA alloc config

- Force gc.collect() before torch.cuda.empty_cache() to ensure all
  model references are released
- Set PYTORCH_CUDA_ALLOC_CONF=expandable_segments:True in container

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

kischdle/llmux/llmux/backends/transformers_llm.py

@@ -45,12 +45,18 @@ class TransformersLLMBackend(BaseBackend):
     async def unload(self, model_id: str) -> None:
         if model_id not in self._loaded:
             return
+        import gc
         entry = self._loaded.pop(model_id)
-        del entry["model"]
-        del entry["tokenizer"]
-        if entry.get("processor"):
-            del entry["processor"]
+        model = entry.pop("model")
+        tokenizer = entry.pop("tokenizer")
+        processor = entry.pop("processor", None)
+        del model
+        del tokenizer
+        del processor
+        del entry
+        gc.collect()
         torch.cuda.empty_cache()
+        logger.info(f"Unloaded {model_id}, VRAM freed")
 
     async def generate(self, model_id, messages, params, stream=False, tools=None):
         entry = self._loaded[model_id]