Add Gemma chat framing

Gemma doesn't have specific support for system prompts but adding it to
the first user prompt seems to work.

src/run.c

@@ -322,6 +322,9 @@ static const char* chatframe(const char* style, bool has_system) {
 	} else if (strcmp(style, "qwen2") == 0) {
 		return has_system ? "<|im_start|>system\n%s<|im_end|>\n<|im_start|>user\n%s<|im_end|>\n<|im_start|>assistant\n"
 		                  : "\n<|im_start|>user\n%s<|im_end|>\n<|im_start|>assistant\n";
+	} else if (strcmp(style, "gemma") == 0) {
+		return has_system ? "<start_of_turn>user\nSYSTEM: %s\n%s<end_of_turn>\n<start_of_turn>model\n"
+		                  : "<start_of_turn>user\n%s<end_of_turn>\n<start_of_turn>model\n";
 	} else {
 		return has_system ? "[INST] <<SYS>>\n%s\n<</SYS>>\n\n%s [/INST]" : "[INST] %s [/INST]";
 	}