feat: update upload functionality and permissions for document handling

- Removed the `upsert` option from the file upload in `uploadDoc` function to prevent unintended overwrites.
- Enhanced German translations in `i18n.js` for better clarity and consistency in the admin interface.
- Added new CSS styles for link interactions to improve user experience in `styles.css`.
- Updated Supabase SQL migration to grant additional permissions for anonymous users to insert and update storage objects, ensuring proper functionality during the booking flow.

Co-authored-by: Copilot <copilot@github.com>

frontend/admin.html

@@ -27,7 +27,7 @@
             <button class="btn" type="submit">Anmelden</button>
             <p class="form-feedback error" id="loginError"></p>
             <p style="color:var(--muted);font-size:0.82rem;text-align:center;">
-                Only admins. Self-registration is disabled.
+                Nur für Administratoren. Selbstregistrierung ist deaktiviert.
             </p>
         </form>
     </section>
@@ -61,7 +61,7 @@
         <div class="admin-bar">
             <h1>MC Cars · Admin</h1>
             <div style="display:flex;gap:0.6rem;align-items:center;flex-wrap:wrap;">
-                <a href="index.html" class="btn ghost small" data-i18n="adminNavWebsite">Website</a>
+                <a id="websiteLink" href="/index.html" target="_blank" class="btn ghost small" data-i18n="adminNavWebsite">Website</a>
                 <button class="lang-toggle" type="button" aria-label="Sprache wechseln" style="margin-left:auto;">EN</button>
 
                 <span id="adminWho" style="color:var(--muted);font-size:0.85rem;margin-left:1rem;"></span>
@@ -74,6 +74,7 @@
         <div class="admin-tabs" role="tablist">
             <button class="tab active" data-tab="leads"     role="tab"><span data-i18n="adminLeads">Leads</span> <span id="leadsBadge" class="tab-badge">0</span></button>
             <button class="tab"        data-tab="customers" role="tab"><span data-i18n="adminCustomers">Kunden</span> <span id="customersBadge" class="tab-badge">0</span></button>
+            <button class="tab"        data-tab="orders"    role="tab"><span data-i18n="adminTabOrderHistory">Bestellungen</span> <span id="ordersBadge" class="tab-badge">0</span></button>
             <button class="tab"        data-tab="vehicles"  role="tab" data-i18n="adminVehicles">Fahrzeuge</button>
         </div>
 
@@ -128,6 +129,30 @@
             </div>
         </div>
 
+        <!-- SALES ORDERS -->
+        <div class="tab-panel" id="tab-orders" style="display:none;">
+            <div class="panel">
+                <h2 data-i18n="adminTabOrderHistory">Bestellungen</h2>
+                <table class="admin-table" id="ordersTable">
+                    <thead>
+                        <tr>
+                            <th>Nr.</th>
+                            <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>Kaution</th>
+                            <th>Miete</th>
+                            <th data-i18n="adminStatus">Status</th>
+                            <th></th>
+                        </tr>
+                    </thead>
+                    <tbody></tbody>
+                </table>
+                <p id="ordersEmpty" class="muted" style="display:none;text-align:center;padding:2rem 0;">Keine Bestellungen.</p>
+            </div>
+        </div>
+
         <!-- VEHICLES -->
         <div class="tab-panel" id="tab-vehicles" style="display:none;">
             <div class="admin-grid">
@@ -215,6 +240,16 @@
         </div>
     </section>
 
+    <!-- Order detail dialog -->
+    <dialog id="orderDialog">
+        <div class="dialog-head">
+            <h3 id="orderDialogTitle" style="margin:0;">Bestellung</h3>
+            <button class="dialog-close" id="orderDialogClose" aria-label="Close">×</button>
+        </div>
+        <div class="dialog-body" id="orderDialogBody"></div>
+        <div class="dialog-footer" id="orderDialogFooter"></div>
+    </dialog>
+
     <!-- Lead detail / qualify dialog (tabbed) -->
     <dialog id="leadDialog">
         <div class="dialog-head">