Add user authentication and registration features

- Implement login and registration HTML templates for user authentication.
- Create user management functions in user.py for handling user data, including adding, deleting, and updating users.
- Introduce password hashing and strength checking for secure user credentials.
- Add terms of service and privacy policy pages to the website.
- Enhance main page with dynamic content based on user session status.

Website/data/appointments.json

@@ -0,0 +1,16 @@
+[
+  {
+    "id": "a-1774281965267",
+    "username": "Aiirondev",
+    "display_name": "Maximilian Gr\u00fcndinger",
+    "date": "2026-03-24",
+    "time": "10:00",
+    "subject": "Test",
+    "note": "",
+    "status": "Abgelehnt",
+    "created_at": "2026-03-23T16:06:05Z",
+    "response": "Es geht leider nicht um die von ihnen angefragte Uhrzeit, bitte versuchen sie es zwei Tage sp\u00e4ter",
+    "responded_at": "2026-03-23T16:06:52Z",
+    "responded_by": "Aiirondev"
+  }
+]