Add practical examples to multiple files

- LF9-03 Virtualisierung: Docker Compose + Volume examples
- LF6-02 Frontend: To-Do list practical example
- LF8-04 ETL: Complete ETL pipeline example
- LF6-04 Sicherheit: Express.js security headers
- LF2-04 Nutzwertanalyse: Cloud provider selection example
- LF9-04 Monitoring: Prometheus alerts + Python logging

1-Ausbildungsjahr/LF6-Webanwendungen/LF6-02-Frontend.md

@@ -99,6 +99,45 @@ element.setAttribute("class", "neu");
 element.getAttribute("href");
 ```
 
+### Praktisches Beispiel: To-Do-Liste
+
+```html
+<!-- HTML -->
+<input type="text" id="todo-input" placeholder="Neue Aufgabe">
+<button id="add-btn">Hinzufügen</button>
+<ul id="todo-list"></ul>
+```
+
+```javascript
+// JavaScript
+const input = document.getElementById('todo-input');
+const button = document.getElementById('add-btn');
+const list = document.getElementById('todo-list');
+
+button.addEventListener('click', () => {
+    const text = input.value.trim();
+    if (text) {
+        // Neues Element erstellen
+        const li = document.createElement('li');
+        li.textContent = text;
+
+        // Löschen-Button
+        const deleteBtn = document.createElement('button');
+        deleteBtn.textContent = 'X';
+        deleteBtn.onclick = () => li.remove();
+
+        li.appendChild(deleteBtn);
+        list.appendChild(li);
+        input.value = '';
+    }
+});
+
+// Enter-Taste Support
+input.addEventListener('keypress', (e) => {
+    if (e.key === 'Enter') button.click();
+});
+```
+
 ### Events
 
 ```javascript