langs: installer/setup Chinese translation

complete the chinese translation referenced below
https://git.ipfire.org/?p=people/ummeegge/ipfire-2.x.git;a=commit;h=ca149dc8e2e24f3cfcf7bbc1e2333b2b6d43e0e4

Asked ChatGPT to translate English in msgid to msgstr in Chinese and
ChatGPT did the translation automatically with correct format.  copied
from ChatGPT and pasted in po.zh

Signed-off-by: Vincent Li <vincent.mc.li@gmail.com>

src/installer/main.c

@@ -247,6 +247,7 @@ static char* center_string(const char* str, int width) {
 
 #define DEFAULT_LANG "en.utf8"
 #define NUM_LANGS 13
+#define NUM_LANGS 14
 
 static struct lang {
 	const char* code;
@@ -265,6 +266,7 @@ static struct lang {
 	{ "pt.utf8",    "Portuguese (Brasil)" },
 	{ "ru.utf8",    "Русский (Russian)" },
 	{ "tr.utf8",    "Türkçe (Turkish)" },
+	{ "zh.utf8",    "简体中文 (Chinese)" },
 	{ NULL, NULL },
 };