fix: align frontend API calls with backend routes and types

- Backend: rename routes /mealplan→/mealplans, /shoppinglist→/shopping
- Backend: simplify swap/reroll to entry-centric endpoints (by entryId)
- Frontend: fix all interfaces to use string GUIDs instead of numbers
- Frontend: fix field names (weekStart, date, totalAmount) to match backend JSON
- Frontend: shopping toggle by itemName instead of non-existent id
- Frontend: handle 204 No Content on DELETE responses
- Docker-compose: use env vars for DB credentials

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/WeekPlanView.vue

@@ -5,7 +5,7 @@
       <div>
         <h1 class="text-2xl font-bold text-zinc-100">Wochenplan</h1>
         <p v-if="store.currentPlan" class="text-zinc-500 text-sm mt-0.5">
-          {{ formatWeek(store.currentPlan.weekStartDate) }}
+          {{ formatWeek(store.currentPlan.weekStart) }}
         </p>
       </div>
       <button
@@ -62,7 +62,7 @@
         v-for="entry in sortedEntries"
         :key="entry.id"
         :entry="entry"
-        :day-name="getDayName(entry.dayOfWeek)"
+        :day-name="getDayName(entry.date)"
         @swap="openSwapModal(entry)"
         @reroll="handleReroll(entry)"
       />
@@ -121,12 +121,13 @@ const swapEntry = ref<MealPlanEntry | null>(null)
 
 const DAY_NAMES = ['Sonntag', 'Montag', 'Dienstag', 'Mittwoch', 'Donnerstag', 'Freitag', 'Samstag']
 
-function getDayName(dayOfWeek: number): string {
-  return DAY_NAMES[dayOfWeek] ?? `Tag ${dayOfWeek}`
+function getDayName(dateStr: string): string {
+  const d = new Date(dateStr + 'T00:00:00')
+  return DAY_NAMES[d.getDay()] ?? dateStr
 }
 
 const sortedEntries = computed(() => {
-  return [...(store.currentPlan?.entries ?? [])].sort((a, b) => a.dayOfWeek - b.dayOfWeek)
+  return [...(store.currentPlan?.entries ?? [])].sort((a, b) => a.date.localeCompare(b.date))
 })
 
 function formatWeek(dateStr: string): string {
@@ -148,7 +149,7 @@ function openSwapModal(entry: MealPlanEntry): void {
   }
 }
 
-async function handleSwapSelect(recipeId: number): Promise<void> {
+async function handleSwapSelect(recipeId: string): Promise<void> {
   if (!swapEntry.value) return
   await store.swapMeal(swapEntry.value.id, recipeId)
   swapEntry.value = null