feat(fs): Implement Global Custom Save Path

Added a "Global Custom Save Path" configuration option in the Filesystem settings.

Implemented a prioritized save-loading hierarchy: Global Path (if enabled) > Per-Game Custom Path > Default NAND.

Introduced a non-destructive migration tool that allows users to consolidate their existing saves into the new global location.

The migration tool specifically prioritizes per-game custom saves over NAND saves to ensure the most up-to-date data is preserved during consolidation.

The migration process is copy-only; no data is deleted from the source directories, ensuring absolute user data safety.

Maintained compatibility with the existing "Backup Saves to NAND" feature, ensuring saves continue to be mirrored internally if configured.

Signed-off-by: Collecting <collecting@noreply.localhost>

src/citron/game_list.cpp

@@ -1085,7 +1085,7 @@ void GameList::AddGamePopup(QMenu& context_menu, u64 program_id, const std::stri
         QDir old_dir(old_save_path);
         if (old_dir.exists() && !old_dir.isEmpty()) {
             QMessageBox::StandardButton reply = QMessageBox::question(this, tr("Move Save Data"),
-                tr("You have existing save data in the NAND. Would you like to move it to the new custom save path?"),
+                tr("You have existing save data in the NAND. Would you like to move it to the new custom save path? Also for reference, if you'd like to use a Global Custom Save Path for all of your titles instead of setting them manually, you can do so within Emulation -> Configure -> Filesystem."),
                 QMessageBox::Yes | QMessageBox::No | QMessageBox::Cancel);
 
             if (reply == QMessageBox::Cancel) return;