Implement modular report system with 6 report types and composer UI

Refactors the Berichte section from a single hardcoded Jahresbericht into
a modular report-building system. Jahresbericht now uses PDFGenerator for
corporate identity (logo, colors, headers/footers, cover page). 8 reusable
section templates can be freely combined. 6 predefined report templates
(Jahres-, Destinatär-, Grundstücks-, Finanz-, Förder-, Pachtbericht) with
HTML preview and PDF export. New Bericht-Baukasten UI lets users compose
custom reports from individual sections.

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

app/templates/berichte/sektionen/konten_uebersicht.html

@@ -0,0 +1,46 @@
+<!-- Sektion: Konten-&Uuml;bersicht -->
+<div class="section">
+  <h2>Konten&uuml;bersicht</h2>
+
+  <div class="stats-grid">
+    <div class="stat-card">
+      <div class="value">{{ konten_anzahl }}</div>
+      <div class="label">Aktive Konten</div>
+    </div>
+    <div class="stat-card">
+      <div class="value">&#8364;{{ konten_gesamtsaldo|floatformat:2 }}</div>
+      <div class="label">Gesamtsaldo</div>
+    </div>
+  </div>
+
+  {% if konten_liste %}
+  <table>
+    <thead>
+      <tr>
+        <th>Kontoname</th>
+        <th>Bank</th>
+        <th>Kontotyp</th>
+        <th>IBAN</th>
+        <th>Saldo</th>
+      </tr>
+    </thead>
+    <tbody>
+      {% for k in konten_liste %}
+      <tr>
+        <td>{{ k.kontoname }}</td>
+        <td>{{ k.bank_name }}</td>
+        <td>{{ k.get_konto_typ_display }}</td>
+        <td>{{ k.iban|default:"-" }}</td>
+        <td class="amount">&#8364;{{ k.saldo|floatformat:2 }}</td>
+      </tr>
+      {% endfor %}
+    </tbody>
+    <tfoot>
+      <tr style="font-weight: bold; background: #f0f7f4;">
+        <td colspan="4">Gesamtsaldo</td>
+        <td class="amount">&#8364;{{ konten_gesamtsaldo|floatformat:2 }}</td>
+      </tr>
+    </tfoot>
+  </table>
+  {% endif %}
+</div>