relicense and make it REUSE-compliant

src/Board.cpp

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2025 thorium1256
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 #include "Board.h"
 #include <iostream>
 

src/Cell.cpp

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2025 thorium1256
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 #include "Cell.h"
 
 Cell::Cell(int x, int y)

src/Vector2.cpp

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2025 thorium1256
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 #include "Vector2.h"
 
 Vector2::Vector2(int x, int y) : x(x), y(y) {}

src/main.cpp

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2025 thorium1256
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 #include <iostream>
 #include <stdexcept>
 #include <ncursesw/ncurses.h>