uebung_03: implement Task 1 (IntLinkedList) and Task 2 (generic LinkedList)

Doubly linked list with head/tail references for int values (Task 1)
and a generic LinkedList<T>/ListNode<T> version (Task 2). Both
implement add, get, remove, getSize with O(n/2) walks via the
closer-end heuristic. Includes IntLinkedListTest covering empty,
single-element, head/tail/middle removal, and out-of-bounds cases.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

uebung_03/src/ListNode.java

@@ -0,0 +1,11 @@
+public class ListNode<T> {
+    T value;
+    ListNode<T> nextNode;
+    ListNode<T> prevNode;
+
+    public ListNode(T value, ListNode<T> nextNode, ListNode<T> prevNode) {
+        this.value = value;
+        this.nextNode = nextNode;
+        this.prevNode = prevNode;
+    }
+}