feat(demo): add isolated demo environments

apps/demos/models.py

@@ -0,0 +1,39 @@
+from django.conf import settings
+from django.db import models
+
+from core.models.base import BaseModel
+
+
+class DemoEnvironment(BaseModel):
+    class Status(models.TextChoices):
+        ACTIVE = "active", "Active"
+        EXPIRED = "expired", "Expired"
+        CLEANED = "cleaned", "Cleaned"
+
+    owner_user = models.OneToOneField(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="demo_environment",
+    )
+    workspace = models.OneToOneField(
+        "workspaces.Workspace",
+        on_delete=models.CASCADE,
+        related_name="demo_environment",
+    )
+    expires_at = models.DateTimeField()
+    status = models.CharField(max_length=16, choices=Status.choices, default=Status.ACTIVE)
+    seed_version = models.CharField(max_length=32, default="v1")
+    cleaned_at = models.DateTimeField(blank=True, null=True)
+    cleanup_error = models.TextField(blank=True)
+
+    class Meta:
+        db_table = "demo_environment"
+        ordering = ("-created_at",)
+        indexes = [
+            models.Index(fields=["status", "expires_at"], name="demo_status_expires_idx"),
+            models.Index(fields=["owner_user"], name="demo_owner_user_idx"),
+            models.Index(fields=["workspace"], name="demo_workspace_idx"),
+        ]
+
+    def __str__(self):
+        return f"Demo {self.workspace_id} for {self.owner_user_id}"