phase3: add normalized domain schema, admin, services, and multistage docker build

apps/providers/models.py

@@ -0,0 +1,41 @@
+from django.contrib.contenttypes.fields import GenericForeignKey
+from django.contrib.contenttypes.models import ContentType
+from django.db import models
+
+
+class ExternalMapping(models.Model):
+    """Maps internal entities to provider-specific IDs across namespaces."""
+
+    provider_namespace = models.CharField(max_length=80)
+    external_id = models.CharField(max_length=160)
+    external_secondary_id = models.CharField(max_length=160, blank=True)
+
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveBigIntegerField()
+    content_object = GenericForeignKey("content_type", "object_id")
+
+    # Raw payload is kept only for troubleshooting and parsing diagnostics.
+    raw_payload = models.JSONField(default=dict, blank=True)
+    last_seen_at = models.DateTimeField(auto_now=True)
+    is_active = models.BooleanField(default=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(
+                fields=["provider_namespace", "external_id"],
+                name="uq_mapping_provider_external_id",
+            ),
+            models.UniqueConstraint(
+                fields=["provider_namespace", "content_type", "object_id"],
+                name="uq_mapping_provider_entity",
+            ),
+        ]
+        indexes = [
+            models.Index(fields=["provider_namespace", "external_id"]),
+            models.Index(fields=["content_type", "object_id"]),
+            models.Index(fields=["is_active"]),
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.provider_namespace}:{self.external_id}"