feat: document templates with auto-fill from case data (P1)

- Database: kanzlai.document_templates table with RLS policies
- Seed: 4 system templates (Klageerwiderung UPC, Berufungsschrift,
  Mandatsbestätigung, Kostenrechnung)
- Backend: TemplateService (CRUD + render), TemplateHandler with
  endpoints: GET/POST /api/templates, GET/PUT/DELETE /api/templates/{id},
  POST /api/templates/{id}/render?case_id=X
- Template variables: case.*, party.*, tenant.*, user.*, date.*, deadline.*
- Frontend: /vorlagen page with category filters, template detail/editor,
  render flow (select case -> preview -> copy/download), variable toolbar
- Quick action: "Schriftsatz erstellen" button on case detail page
- Also: resolved merge conflicts between audit-trail and role-based branches,
  added missing Notification/AuditLog types to frontend

frontend/src/app/(app)/cases/[id]/layout.tsx

@@ -17,6 +17,7 @@ import {
   StickyNote,
   AlertTriangle,
   ScrollText,
+  FilePlus,
 } from "lucide-react";
 import { format } from "date-fns";
 import { de } from "date-fns/locale";
@@ -171,19 +172,28 @@ export default function CaseDetailLayout({
             {caseDetail.court_ref && <span>({caseDetail.court_ref})</span>}
           </div>
         </div>
-        <div className="text-right text-xs text-neutral-400">
-          <p>
-            Erstellt:{" "}
-            {format(new Date(caseDetail.created_at), "d. MMM yyyy", {
-              locale: de,
-            })}
-          </p>
-          <p>
-            Aktualisiert:{" "}
-            {format(new Date(caseDetail.updated_at), "d. MMM yyyy", {
-              locale: de,
-            })}
-          </p>
+        <div className="flex flex-col items-end gap-2">
+          <Link
+            href={`/vorlagen?case_id=${id}`}
+            className="flex items-center gap-1.5 rounded-md bg-neutral-900 px-3 py-1.5 text-sm font-medium text-white transition-colors hover:bg-neutral-800"
+          >
+            <FilePlus className="h-3.5 w-3.5" />
+            Schriftsatz erstellen
+          </Link>
+          <div className="text-right text-xs text-neutral-400">
+            <p>
+              Erstellt:{" "}
+              {format(new Date(caseDetail.created_at), "d. MMM yyyy", {
+                locale: de,
+              })}
+            </p>
+            <p>
+              Aktualisiert:{" "}
+              {format(new Date(caseDetail.updated_at), "d. MMM yyyy", {
+                locale: de,
+              })}
+            </p>
+          </div>
         </div>
       </div>