🐛 Fix mod sync saving files when nothing changed

[sakuro]

Summary

Fix mod sync incorrectly saving mod-list.json and mod-settings.dat even when nothing changed, causing misleading output like "Nothing to change" followed by "Updated mod-list.json".

Changes

• Skip saving mod-list.json when no MOD list changes are needed
• Skip saving mod-settings.dat when startup settings are unchanged
• Detect actual startup settings changes by comparing save file settings against current mod-settings.dat
• Include startup settings changes in the combined plan and confirmation flow

Before

ℹ Nothing to change
✓ Updated mod-list.json
✓ Updated mod-settings.dat
✓ Sync completed successfully

After

ℹ Nothing to change

Closes #74