i18n: include vector header

[LinuxUserGD]

Fixes the following compilation error on Gentoo Linux amd64 (musl/llvm):

[16/25] /usr/lib/llvm/21/bin/clang++ -DHYPRUTILS_VERSION=\"0.11.0\" -Dhyprutils_EXPORTS -I/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/./include -I/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/./src -isystem /usr/include/pixman-1  -O2 -pipe -stdlib=libc++ -std=gnu++26 -fPIC -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-unused-value -Wno-missing-field-initializers -Wno-narrowing -Wno-pointer-arith -O3 -MD -MT CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o -MF CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o.d -o CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o -c /var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nLocale.cpp
samu: job failed: /usr/lib/llvm/21/bin/clang++ -DHYPRUTILS_VERSION=\"0.11.0\" -Dhyprutils_EXPORTS -I/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/./include -I/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/./src -isystem /usr/include/pixman-1  -O2 -pipe -stdlib=libc++ -std=gnu++26 -fPIC -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-unused-value -Wno-missing-field-initializers -Wno-narrowing -Wno-pointer-arith -O3 -MD -MT CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o -MF CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o.d -o CMakeFiles/hyprutils.dir/src/i18n/I18nLocale.cpp.o -c /var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nLocale.cpp
In file included from /var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nLocale.cpp:1:
/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nEngine.hpp:13:46: error: no member named 'vector' in namespace 'std'
   13 |         std::unordered_map<std::string, std::vector<SI18nTranslationEntry>> entries;
      |                                              ^~~~~~
/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nEngine.hpp:13:53: error: 'SI18nTranslationEntry' does not refer to a value
   13 |         std::unordered_map<std::string, std::vector<SI18nTranslationEntry>> entries;
      |                                                     ^
/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nEngine.hpp:6:12: note: declared here
    6 |     struct SI18nTranslationEntry {
      |            ^
/var/tmp/portage/gui-libs/hyprutils-9999/work/hyprutils-9999/src/i18n/I18nEngine.hpp:13:75: error: expected member name or ';' after declaration specifiers
   13 |         std::unordered_map<std::string, std::vector<SI18nTranslationEntry>> entries;
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
3 errors generated.