feat: rework admin portal with pricing breakdown and document management

- Added pricing snapshot columns to the leads table: daily_subtotal, weekend_subtotal, subtotal_eur, vat_eur, total_eur, deposit_eur, total_days, weekday_count, weekend_day_count.
- Updated create_lead RPC to accept and store new pricing parameters.
- Enhanced frontend app.js to compute and send pricing details during lead creation.
- Introduced new UI elements in admin.html for displaying pricing and documents in a tabbed dialog.
- Updated i18n.js with new translation keys for pricing and document management.
- Improved styles in styles.css for new dialog components and pricing cards.
- Added migration script 06-admin-pricing-documents.sql for database schema changes.

frontend/admin.html

@@ -94,6 +94,7 @@
                             <th data-i18n="adminNameEmail">Name / E-Mail</th>
                             <th data-i18n="adminVehicleTab">Fahrzeug</th>
                             <th data-i18n="adminPeriod">Zeitraum</th>
+                            <th data-i18n="adminTotalPrice">Gesamtbetrag</th>
                             <th data-i18n="adminStatus">Status</th>
                             <th></th>
                         </tr>
@@ -116,6 +117,7 @@
                             <th data-i18n="adminNameEmail">Name / E-Mail</th>
                             <th data-i18n="adminPhone">Telefon</th>
                             <th data-i18n="adminSourceLead">Quelle (Lead)</th>
+                            <th data-i18n="adminLifetimeValueCol">Gesamtwert</th>
                             <th data-i18n="adminStatus">Status</th>
                             <th></th>
                         </tr>
@@ -213,13 +215,26 @@
         </div>
     </section>
 
-    <!-- Lead detail / qualify dialog -->
+    <!-- Lead detail / qualify dialog (tabbed) -->
     <dialog id="leadDialog">
         <div class="dialog-head">
             <h3 id="leadDialogTitle" style="margin:0;">Lead</h3>
             <button class="dialog-close" id="leadDialogClose" aria-label="Close">×</button>
         </div>
+        <div class="dialog-tabs" id="leadDialogTabs" role="tablist"></div>
         <div class="dialog-body" id="leadDialogBody"></div>
+        <div class="dialog-footer" id="leadDialogFooter"></div>
+    </dialog>
+
+    <!-- Customer detail dialog (tabbed) -->
+    <dialog id="customerDialog">
+        <div class="dialog-head">
+            <h3 id="customerDialogTitle" style="margin:0;">Kunde</h3>
+            <button class="dialog-close" id="customerDialogClose" aria-label="Close">×</button>
+        </div>
+        <div class="dialog-tabs" id="customerDialogTabs" role="tablist"></div>
+        <div class="dialog-body" id="customerDialogBody"></div>
+        <div class="dialog-footer" id="customerDialogFooter"></div>
     </dialog>
 
     <script type="module" src="admin.js"></script>