Implement tamper-evident audit logging and invoice correction features

- Introduced a new audit logging system that creates a tamper-evident chain of events in MongoDB.
- Added functions for appending audit events, ensuring index integrity, and verifying the audit chain.
- Implemented soft-delete functionality for inventory and borrowing records to comply with GoBD regulations.
- Added UI components for displaying invoice corrections and audit dashboard, including mismatch reporting.
- Created a CLI utility for verifying the integrity of the audit chain.
- Enhanced invoice management by preventing overwrites and allowing correction entries with reasons and optional deltas.

Web/templates/base.html

@@ -418,6 +418,7 @@
                             <li><a class="dropdown-item" href="{{ url_for('manage_filters') }}">Filter verwalten</a></li>
                             <li><a class="dropdown-item" href="{{ url_for('manage_locations') }}">Orte verwalten</a></li>
                             <li><a class="dropdown-item" href="{{ url_for('admin_borrowings') }}">Ausleihen</a></li>
+                            <li><a class="dropdown-item" href="{{ url_for('admin_audit_dashboard') }}">Audit Dashboard</a></li>
                             <li><a class="dropdown-item" href="{{ url_for('logs') }}">Logs</a></li>
                             <li><hr class="dropdown-divider"></li>
                             <li><h6 class="dropdown-header">System</h6></li>