feat(logs): admin changes and logins are recorded on the Logs page

The Logs page shows who added, changed or deleted a compute, from web
or API, and every login, failed login, lockout and logout, with the
client address and a Result column (Done, Failed, Unknown for older
rows). A failed change is recorded with its reason and the error still
reaches the user; a refused one is recorded too.

- logs.audit.write saves each row in its own savepoint and never
  raises, so a log write cannot break or undo the action it records.
  The audit() context manager writes one row when the change ends.
- Logs gains success and ip; user, host and instance are wider and
  date is indexed. The page orders by date then id.
- A compute edit names the changed fields; an edit that changes
  nothing writes no row, and an empty password field is no change.
- A compute's VMs leaving the panel get a system row each: owners
  kept on the Removed VMs page, moved to another compute, restored,
  left without owners, or the removed record expired.
- Job rows carry the result. A job's log entry that cannot be
  computed is logged and skipped instead of rolling back the finish
  (test_service.py changes this on purpose).
- Logins are recorded by signal receivers; CustomLoginView is removed
  and the plain LoginView is used. A wrong OTP code is a failed login,
  counted by django-axes toward the lockout.

Panel records and host-side objects follow in the next layers.

computes/api/viewsets.py

@@ -2,6 +2,7 @@ from admin.permissions import IsSuperUser
 from computes.models import Compute
 from drf_spectacular.types import OpenApiTypes
 from drf_spectacular.utils import extend_schema
+from logs.audit import audit, changed_fields, snapshot
 from rest_framework import viewsets
 from rest_framework.response import Response
 from vrtManager.create import wvmCreate
@@ -19,6 +20,25 @@ class ComputeViewSet(viewsets.ModelViewSet):
     serializer_class = ComputeSerializer
     permission_classes = [IsSuperUser]
 
+    def perform_create(self, serializer):
+        data = serializer.validated_data
+        with audit(self.request, data["name"], f"Compute {data['name']} ({data['hostname']})", "add"):
+            serializer.save()
+
+    def perform_update(self, serializer):
+        compute = serializer.instance
+        subject = f"Compute {compute.name} ({compute.hostname})"
+        before = snapshot(compute)
+        with audit(self.request, compute, subject, "change") as entry:
+            serializer.save()
+            fields = changed_fields(before, snapshot(compute))
+            entry.action = "change " + ", ".join(fields)
+            entry.skip = not fields
+
+    def perform_destroy(self, instance):
+        with audit(self.request, instance, f"Compute {instance.name} ({instance.hostname})", "delete"):
+            instance.delete()
+
 
 class ComputeArchitecturesView(viewsets.ViewSet):
     permission_classes = [IsSuperUser]