Add M365 License Calculator feature

New top-nav section with a CSV-based license calculator. Upload an Azure AD
user export to see license counts (M365 Standard/Basic, Defender P1, PBI Pro,
PBI Premium) grouped by QWE Client. QWE Client and IsRestaurant are editable
per user, saved to SQLite, and restored on the next upload. Department-based
defaults pre-populate QWE Client (AT→QWE AT, SK→QWE SK) when no saved value
exists.

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

app/templates/base.html

@@ -50,6 +50,11 @@
                       {% if request.url.path == '/audit' %}bg-gray-100 text-gray-900{% else %}text-gray-600 hover:text-gray-900 hover:bg-gray-100{% endif %}">
               Audit Log
             </a>
+            <a href="/m365/license-calculator"
+               class="px-3 py-2 rounded-md text-sm font-medium transition-colors
+                      {% if request.url.path.startswith('/m365') %}bg-gray-100 text-gray-900{% else %}text-gray-600 hover:text-gray-900 hover:bg-gray-100{% endif %}">
+              M365
+            </a>
           </div>
         </div>
         {% if user %}