add credits link to starting modal (#2333)

## Description:

* Create CREDITS.md
* add all link to it on loading page

<img width="338" height="254" alt="Screenshot 2025-10-30 at 6 24 07 PM"
src="https://github.com/user-attachments/assets/5e89c846-f672-44e1-9add-3d03608c849e"
/>


## 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

CREDITS.md

@@ -0,0 +1,28 @@
+# Credits
+
+## Code
+
+OpenFront is licensed under AGPL-3.0.  
+See [Contributors](https://github.com/openfrontio/OpenFrontIO/graphs/contributors) for code contributors.
+
+## Map Data
+
+### OpenStreetMap
+
+© [OpenStreetMap contributors](https://www.openstreetmap.org/copyright)  
+Licensed under ODbL
+
+### Natural Earth
+
+[Natural Earth](https://www.naturalearthdata.com/)  
+Public Domain
+
+### Bedmap3 Antarctica Dataset
+
+Pritchard, H.D., Fretwell, P.T., Fremand, A.C. et al. Bedmap3 updated ice bed, surface and thickness gridded datasets for Antarctica. _Sci Data_ 12, 109 (2025).  
+[https://doi.org/10.1038/s41597-025-04672-y](https://doi.org/10.1038/s41597-025-04672-y)  
+Licensed under [CC-BY 4.0](https://creativecommons.org/licenses/by/4.0/)
+
+## Icons
+
+Icons from [The Noun Project](https://thenounproject.com/)