Update ollama/ollama Docker tag to v0.15.3

Author: renovate[bot]

nix/hosts/mentat/modules/stacks/ai.nix

@@ -35,7 +35,7 @@ in
       containers = {
         ollama = {
           containerConfig = {
-            image = "ollama/ollama:0.14.1";
+            image = "ollama/ollama:0.15.3";
             devices = [ "nvidia.com/gpu=all" ];
             publishPorts = [ "${toString ollama.port}:11434" ];
             volumes = [ "/root/.ollama:/root/.ollama" ];