✨(backend) introduce Recording model with independent access control

The Recording model is introduced to track recording lifecycle within rooms,
while maintaining strict separation of access controls between rooms and
recordings.

Recordings follow the BaseAccess pattern (similar to Documents in Impress),
providing independent access control from room permissions. This ensures that
joining a room doesn't automatically grant access to previous recordings,
allowing for more flexible permission management.

The implementation was driven by TDD, particularly for the get_abilities
function, resulting in reduced nesting levels and improved readability.

The Recording model is deliberately kept minimal to serve as a foundation for
upcoming AI features while maintaining flexibility for future extensions.

I have avoided LiveKit-specific terminology for better abstraction.

Note: Room access control remains unchanged in this commit, pending future
refactor to use BaseAccess pattern (discussed IRL with @sampaccoud).

src/backend/core/factories.py

@@ -65,3 +65,48 @@ class RoomFactory(ResourceFactory):
 
     name = factory.Faker("catch_phrase")
     slug = factory.LazyAttribute(lambda o: slugify(o.name))
+
+
+class RecordingFactory(factory.django.DjangoModelFactory):
+    """Create fake recording for testing."""
+
+    class Meta:
+        model = models.Recording
+
+    room = factory.SubFactory(RoomFactory)
+    status = models.RecordingStatusChoices.INITIATED
+    worker_id = None
+
+    @factory.post_generation
+    def users(self, create, extracted, **kwargs):
+        """Add users to recording from a given list of users with or without roles."""
+        if create and extracted:
+            for item in extracted:
+                if isinstance(item, models.User):
+                    UserRecordingAccessFactory(recording=self, user=item)
+                else:
+                    UserRecordingAccessFactory(
+                        recording=self, user=item[0], role=item[1]
+                    )
+
+
+class UserRecordingAccessFactory(factory.django.DjangoModelFactory):
+    """Create fake recording user accesses for testing."""
+
+    class Meta:
+        model = models.RecordingAccess
+
+    recording = factory.SubFactory(RecordingFactory)
+    user = factory.SubFactory(UserFactory)
+    role = factory.fuzzy.FuzzyChoice(models.RoleChoices.values)
+
+
+class TeamRecordingAccessFactory(factory.django.DjangoModelFactory):
+    """Create fake recording team accesses for testing."""
+
+    class Meta:
+        model = models.RecordingAccess
+
+    recording = factory.SubFactory(RecordingFactory)
+    team = factory.Sequence(lambda n: f"team{n}")
+    role = factory.fuzzy.FuzzyChoice(models.RoleChoices.values)