[HIGH] Missing .env validation causes wrong HTTP request

MODEL_NAME, HF_TO_GGUF, GGUF_FILE imported from @env. If .env is missing, HF_TO_GGUF is undefined and downloadModel constructs https://huggingface.co/undefined/resolve/main/... - makes request to wrong URL.\n\nFile: Frontend/src/model/model.jsx, lines 6, 38, 71\nFix: Add null checks: if (!HF_TO_GGUF) throw new Error("HF_TO_GGUF not configured")