refactor: migrate all page.server.ts files to typed API client

All server-side fetch calls now go through createApiClient() from
$lib/api.server.ts, which wraps openapi-fetch with the generated OpenAPI
types. This means backend changes are reflected in the frontend after
running npm run generate:api.

- Add stub src/lib/generated/api.ts (replaced by generate:api output)
- Fix GroupController: missing /api prefix and ResponseStatusException
- Root, conversations, persons, documents pages all use typed client
- Error handling uses apiError.code directly (no parseBackendError needed)
- Edit page load uses typed client; PUT action keeps raw fetch (multipart)
- Login keeps raw fetch (explicit Authorization header, not cookie auth)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/conversations/+page.server.ts

@@ -1,62 +1,61 @@
-import { env } from '$env/dynamic/private';
+import { createApiClient } from '$lib/api.server';
 
 export async function load({ url, fetch }) {
-    
-
-    const baseUrl = env.API_INTERNAL_URL || 'http://localhost:8080';
-
-    // 1. Parameter auslesen
     const senderId = url.searchParams.get('senderId') || '';
     const receiverId = url.searchParams.get('receiverId') || '';
     const from = url.searchParams.get('from') || '';
     const to = url.searchParams.get('to') || '';
     const dir = url.searchParams.get('dir') || 'DESC';
 
-    let documents = [];
+    const api = createApiClient(fetch);
+
+    let documents: unknown[] = [];
     let senderName = '';
     let receiverName = '';
 
-    // 2. Fetch-Requests vorbereiten
-    const requests = [];
+    const requests: Promise<void>[] = [];
 
-    // Dokumente laden (nur wenn beide IDs da sind)
     if (senderId && receiverId) {
-        const query = new URLSearchParams({ senderId, receiverId, dir });
-        if (from) query.set('from', from);
-        if (to) query.set('to', to);
         requests.push(
-            fetch(`${baseUrl}/api/documents/conversation?${query}`)
-                .then(r => r.ok ? r.json() : [])
-                .then(data => documents = data)
+            api.GET('/api/documents/conversation', {
+                params: {
+                    query: {
+                        senderId,
+                        receiverId,
+                        dir,
+                        from: from || undefined,
+                        to: to || undefined
+                    }
+                }
+            }).then(({ data }) => { documents = data ?? []; })
         );
     }
 
-    // Namen auflösen für Typeahead Initial Value
     if (senderId) {
         requests.push(
-            fetch(`${baseUrl}/api/persons/${senderId}`)
-                .then(r => r.ok ? r.json() : null)
-                .then(p => senderName = p ? `${p.firstName} ${p.lastName}` : '')
+            api.GET('/api/persons/{id}', { params: { path: { id: senderId } } })
+                .then(({ data }) => {
+                    const p = data as { firstName: string; lastName: string } | undefined;
+                    if (p) senderName = `${p.firstName} ${p.lastName}`;
+                })
         );
     }
 
     if (receiverId) {
         requests.push(
-            fetch(`${baseUrl}/api/persons/${receiverId}`)
-                .then(r => r.ok ? r.json() : null)
-                .then(p => receiverName = p ? `${p.firstName} ${p.lastName}` : '')
+            api.GET('/api/persons/{id}', { params: { path: { id: receiverId } } })
+                .then(({ data }) => {
+                    const p = data as { firstName: string; lastName: string } | undefined;
+                    if (p) receiverName = `${p.firstName} ${p.lastName}`;
+                })
         );
     }
 
-    // Alles parallel abfeuern
     await Promise.all(requests);
 
     return {
         documents,
-        initialValues: {
-            senderName,
-            receiverName
-        },
+        initialValues: { senderName, receiverName },
         filters: { senderId, receiverId, from, to, dir }
     };
 }