ai: Use Q8_K_XL as the default model precision.

It offers faster performance and reasonably accurate responses.

src/ui/interface.py

@@ -29,7 +29,7 @@ def ui():
                     "The smaller the value, the faster the response but less accurate. "
                     "Conversely, the larger the value, the response is slower but more accurate."
                 ),
-                value="F16"  # Default selected precision value
+                value="Q8_K_XL"  # Default selected precision value
             )
 
             # Checkbox to enable or disable reasoning mode, which toggles the AI's "thinking" capability