feat: Package 4 Phase 2 — Frontend-Fixes und Backend-Endpoints vervollständigt

- document-generator: STEP_EXPLANATIONS Key 'consent' → 'document-generator'
- Proxy: Content-Type nicht mehr hardcoded; forwarded vom Client (Fix für DOCX-Upload + multipart/arrayBuffer)
- Backend: GET /documents/{id}, DELETE /documents/{id}, GET /versions/{id} ergänzt
- Backend-Tests: 4 neue Tests für die neuen Endpoints
- consent/page.tsx: Create-Modal + handleCreateDocument() + DELETE-Handler verdrahtet
- einwilligungen/page.tsx: odentifier→identifier, ip_address, user_agent, history aus API gemappt; source nullable
- cookie-banner/page.tsx: handleExportCode() + Toast für 'Code exportieren' Button
- workflow/page.tsx: 'Neues Dokument' Button + createDocument() + Modal

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

admin-compliance/app/api/admin/consent/[[...path]]/route.ts

@@ -22,9 +22,9 @@ async function proxyRequest(
     : `${basePath}${searchParams ? `?${searchParams}` : ''}`
 
   try {
-    const headers: HeadersInit = {
-      'Content-Type': 'application/json',
-    }
+    const headers: HeadersInit = {}
+    const contentType = request.headers.get('Content-Type')
+    if (contentType) headers['Content-Type'] = contentType
 
     const headerNames = ['authorization', 'x-namespace-id', 'x-tenant-slug']
     for (const name of headerNames) {
@@ -47,9 +47,17 @@ async function proxyRequest(
     }
 
     if (method === 'POST' || method === 'PUT') {
-      const body = await request.text()
-      if (body) {
-        fetchOptions.body = body
+      const isMultipart = contentType?.includes('multipart/form-data')
+      if (isMultipart) {
+        const buffer = await request.arrayBuffer()
+        if (buffer.byteLength > 0) {
+          fetchOptions.body = buffer
+        }
+      } else {
+        const body = await request.text()
+        if (body) {
+          fetchOptions.body = body
+        }
       }
     }