clarify license (#1277)

## Description:

Use full GPL license in LICENSE-GPL for clarity
Put both MIT & GPL in LICENSE & specify when src/client was changed from
MIT => GPT

## 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
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

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

DISCORD_USERNAME

LICENSE

@@ -1,6 +1,13 @@
-MIT License
+License Information for OpenFront.io Project
+Overview
+As of commit 25d5cc370207fd39e0c3bcaa69873b8fc6c60e68, the src/client directory of the OpenFront.io project has been relicensed from the MIT License to the GNU General Public License (GPL) version 3.0. The rest of the project remains under the MIT License unless otherwise specified. Below are the details of both licenses and their applicability.
 
-Copyright (c) 2025 OpenFront.io Team
+## MIT License
+   Applies to: All parts of the OpenFront.io project except the src/client directory as of commit 25d5cc370207fd39e0c3bcaa69873b8fc6c60e68 (March 25 2025).
+   MIT License
+
+Portions Copyright (c) 2024 WarFront.io Team
+Portions Copyright (c) 2024 OpenFront.io Team
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -19,3 +26,34 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
+
+## GNU General Public License (GPL) version 3.0
+   Applies to: The src/client directory as of commit 25d5cc370207fd39e0c3bcaa69873b8fc6c60e68.
+   GNU GENERAL PUBLIC LICENSE
+   Version 3, 29 June 2007
+
+Copyright (c) 2025 OpenFront.io Team
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+[Full text of the GPL v3.0 license can be found in src/client/LICENSE-GPL, or at  <https://www.gnu.org/licenses/gpl-3.0.txt>]
+
+## Important Notes
+
+MIT License: A permissive license that allows users to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the software with minimal restrictions, provided the copyright notice and permission notice are included.
+GPL v3.0: A copyleft license that requires any derivative works or distributions of the src/client code to also be licensed under GPL v3.0 or later, ensuring that the source code remains open and freely available.
+If you are combining code from src/client (GPL) with other parts of the project (MIT), the GPL’s copyleft requirements may affect the licensing of the combined work. Consult a legal expert for specific guidance.
+For contributions to src/client, ensure that all contributors agree to the GPL v3.0 terms.
+
+For any questions, contact the OpenFront.io Team.