Update license: AGPL & CC SA (#2009)

## Description:

Update project license: all code agpl v3, all assets: CC-SA

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

LICENSE-ASSETS

@@ -0,0 +1,19 @@
+# Asset License - Creative Commons BY-SA 4.0
+
+This license applies to all non-code assets in this repository, including but not limited to:
+- Graphics, sprites, and images (*.png, *.jpg, *.svg, etc.)
+- 3D models and textures (*.obj, *.fbx, *.blend, etc.)
+- Audio files (*.mp3, *.ogg, *.wav, etc.)
+- Animation files
+- Font files
+- Level/map data files
+
+This license does NOT apply to:
+- Source code files (*.js, *.ts, *.py, etc.) - see LICENSE for code licensing
+- Configuration files that contain code
+- Scripts and shaders
+
+Attribution required: "OpenFront.io" or "OpenFront LLC"
+
+To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/4.0/
+or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.