Signature image in cover letter + fix per-paragraph capitalization

- Only the first body paragraph continues the salutation (lowercase safe
  opener); every following paragraph is a new sentence and is capitalized.
  Handled deterministically so it no longer depends on the model.
- Signature: upload a signature image on the Vorlagen page (preview / replace /
  remove). It is embedded in the cover letter directly under the closing
  salutation, replacing the typed name; falls back to the name when absent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

views/vorlagen.ejs

@@ -183,6 +183,40 @@
                 </div>
             </form>
         </section>
+
+        <!-- Signature -->
+        <h2 class="text-xl font-bold text-gray-800 dark:text-white mt-10 mb-2">Unterschrift</h2>
+        <p class="text-sm text-gray-500 dark:text-gray-400 mb-6">
+            Lade dein Unterschriftsbild (PNG/JPG, am besten mit transparentem Hintergrund) hoch. Es wird im
+            Anschreiben direkt unter „Mit freundlichen Grüßen" anstelle des getippten Namens eingefügt.
+        </p>
+
+        <section class="bg-white dark:bg-gray-800 rounded-lg shadow-md p-6 mb-6">
+            <% if (hasSignatur) { %>
+                <div class="flex items-center justify-between gap-4 mb-4">
+                    <div class="rounded-lg border border-gray-200 dark:border-gray-700 bg-gray-50 dark:bg-gray-700/40 p-3">
+                        <img src="/unterschrift?t=<%= Date.now() %>" alt="Unterschrift" class="max-h-24 max-w-[240px] object-contain">
+                    </div>
+                    <form action="/unterschrift/delete" method="POST" onsubmit="return confirm('Unterschrift entfernen?');">
+                        <button type="submit" class="text-sm text-red-600 hover:text-red-800 dark:text-red-400 hover:underline">Entfernen</button>
+                    </form>
+                </div>
+            <% } else { %>
+                <p class="text-sm text-gray-500 dark:text-gray-400 mb-4">Noch keine Unterschrift hinterlegt.</p>
+            <% } %>
+
+            <form action="/unterschrift" method="POST" enctype="multipart/form-data"
+                  class="border-t border-gray-200 dark:border-gray-700 pt-4 mt-2 flex flex-wrap items-end gap-3">
+                <div class="flex-1 min-w-[220px]">
+                    <label class="block text-xs font-medium text-gray-500 dark:text-gray-400 mb-1">Unterschrift-Bild (PNG/JPG)</label>
+                    <input type="file" name="signatur" accept="image/png,image/jpeg" required
+                        class="w-full text-sm text-gray-700 dark:text-gray-300 file:mr-3 file:py-2 file:px-3 file:rounded-md file:border-0 file:bg-blue-600 file:text-white hover:file:bg-blue-700">
+                </div>
+                <button type="submit" class="px-4 py-2 bg-green-600 hover:bg-green-700 text-white rounded-md transition-colors">
+                    <%= hasSignatur ? 'Ersetzen' : 'Hochladen' %>
+                </button>
+            </form>
+        </section>
     </main>
 
     <%- include('partials/footer') %>