feat(io): MapView model (CellState, RoomCell, Connection, MapView)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/src/test/java/thb/jeanluc/adventure/io/text/MapViewTest.java

@@ -0,0 +1,17 @@
+package thb.jeanluc.adventure.io.text;
+
+import org.junit.jupiter.api.Test;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class MapViewTest {
+    @Test
+    void mapViewIsImmutableAndHoldsCellsAndConnections() {
+        RoomCell a = new RoomCell("kitchen", "Kitchen", 0, 0, CellState.CURRENT);
+        RoomCell b = new RoomCell("hallway", "Hallway", 0, -1, CellState.VISITED);
+        MapView v = new MapView(List.of(a, b), List.of(new Connection(a, b)));
+        assertThat(v.cells()).hasSize(2);
+        assertThat(v.connections()).hasSize(1);
+        assertThat(v.connections().getFirst().from().id()).isEqualTo("kitchen");
+    }
+}