Add license and README, document GIF cape + backend integration, cache CI

LICENSE

@@ -0,0 +1,21 @@
+HDSkinSupportGravit License
+
+Copyright (c) 2026 Nghtly
+
+Permission is hereby granted, free of charge, to any person to use, copy,
+modify, merge, publish, and distribute this software and its source code, in
+whole or in part, for any purpose.
+
+Condition for commercial use:
+  Any commercial use, distribution, or product (paid, monetized, or as part of a
+  paid service) that includes this software or a work derived from it must give
+  visible credit to the original author, "Nghtly" — for example in the product
+  description, credits screen, or accompanying documentation.
+
+Non-commercial use carries no attribution requirement.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE, AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHOR BE
+LIABLE FOR ANY CLAIM, DAMAGES, OR OTHER LIABILITY ARISING FROM, OUT OF, OR IN
+CONNECTION WITH THE SOFTWARE OR ITS USE.