The online update always pulls every preset Celestrak/amsat URL and
the custom URL lived hidden behind the "Import" dialog's toggle. The
user wants a discoverable entry point to edit the custom source URLs.
Rename the data card button "Import" -> "Custom URL" (en: Custom URL,
zh: 自定义URL, tr: Özel URL). The existing dialog already hosts both
URL text fields (TLE + transceivers) and the file-import buttons, so
no dialog changes are needed - the import feature stays inside, as
the user requested.
Version bump per fork convention (feature change): 4.4.7 -> 4.4.8,
versionCode 447 -> 448. v4.4.7 release stays downloadable.
What's-new dialog updated in all three locales with this change.
Verified: settings + app compile, unit tests unaffected.