Add JWT auth with per-user data isolation and account settings.

Users can register, log in, and manage profile/password in a personal account page; server data is scoped by owner across contacts, maps, tags, and import.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/core/drf_mixins.py

@@ -0,0 +1,16 @@
+from rest_framework.permissions import AllowAny, IsAuthenticated
+from rest_framework_simplejwt.authentication import JWTAuthentication
+
+from core.access import use_jwt_auth
+
+
+class JwtAuthMixin:
+    def get_permissions(self):
+        if use_jwt_auth():
+            return [IsAuthenticated()]
+        return [AllowAny()]
+
+    def get_authenticators(self):
+        if use_jwt_auth():
+            return [JWTAuthentication()]
+        return super().get_authenticators()