STAT3 and hepatocellular carcinoma: Critical metabolites such as bile acids, short-chain fatty acids, lipopolysaccharide, polyamines, and trimethylamine N-oxide (TMAO) regulate HCC progression by remodeling the tumor immune microenvironment, reprogramming immunometabolism, and modulating core signaling pathways including NF-κB, STAT3, and mTOR.