Implement environment variable setup for frontend; create .env.production and .env.development files if they don't exist, and update API URLs in frontend components to use dynamic API_BASE_URL for improved configuration management.

frontend/src/views/Timefix.vue

@@ -179,7 +179,7 @@ async function loadWorklogEntries() {
     if (!date) return
     
     // Hole alle Worklog-Einträge für das Datum vom Backend
-    const response = await fetch(`http://localhost:3010/api/timefix/worklog-entries?date=${date}`, {
+    const response = await fetch(`${API_URL}/timefix/worklog-entries?date=${date}`, {
       headers: authStore.getAuthHeaders()
     })
     
@@ -224,7 +224,7 @@ function onEntrySelected() {
 async function loadTimefixes() {
   try {
     loading.value = true
-    const response = await fetch('http://localhost:3010/api/timefix', {
+    const response = await fetch('${API_URL}/timefix', {
       headers: authStore.getAuthHeaders()
     })
     
@@ -248,7 +248,7 @@ async function createTimefix() {
   
   try {
     loading.value = true
-    const response = await fetch('http://localhost:3010/api/timefix', {
+    const response = await fetch('${API_URL}/timefix', {
       method: 'POST',
       headers: {
         ...authStore.getAuthHeaders(),
@@ -290,7 +290,7 @@ async function deleteTimefix(id) {
   
   try {
     loading.value = true
-    const response = await fetch(`http://localhost:3010/api/timefix/${id}`, {
+    const response = await fetch(`${API_URL}/timefix/${id}`, {
       method: 'DELETE',
       headers: authStore.getAuthHeaders()
     })