fix(mem): enforce C locale for free command output parsing

[heysion]

Prefix the free command with LC_ALL=C in detectmem() so that its output format stays consistent regardless of the user's locale, preventing awk parsing from breaking on localized environments.

Log: Fix locale-dependent memory detection parsing on Linux

Influence:

1. Memory detection output on non-English Linux locales
2. RAM usage display correctness in detectmem() Linux branch

./screenfetch-dev: 行 1892: -: 语法错误：需要操作数（错误记号是 "-"）
         _,met$$$$$gg.           heysion@sysnpc
      ,g$$$$$$$$$$$$$$$P.        OS: Debian 13 trixie
   ,g$$P""       """Y$$.".      Kernel: x86_64 Linux 6.12.94+deb13-amd64
 ,$$P'              `$$$.      Uptime: 2d 12h 31m
  ',$$P       ,ggs.     `$$b:    Packages: 4669
  `d$$'     ,$P"'   .    $$$     Shell: bash
   $$P      d$'     ,    $$P     Resolution: 2560x2520
   $$:      $$.   -    ,d$$'     DE: GNOME 48.4
   $$\;      Y$b._   _,d$P'      WM: Mutter
   Y$$.    `.`"Y$$$$P"'          WM Theme: 
   `$$b      "-.__               GTK Theme: Ant [GTK2/3]
    `Y$$                         Icon Theme: Papirus-Light
     `Y$$.                       Font: Noto Sans Mono 12
       `$$b.                     Disk: 721G / 1.1T (73%)
         `Y$$b.                  CPU: Intel Core i5-1035G7 @ 8x 3.7GHz [63.0°C]
            `"Y$b._              GPU: Mesa Intel(R) Iris(R) Plus Graphics (ICL GT2)
                `""""            RAM: -