Add canonical field and update synonym handling in Condition model

- Introduced a new `canonical` ForeignKey field in the Condition model to manage alias relationships.
- Enhanced synonym retrieval methods to prefer canonical names and handle aliases more effectively.
- Updated condition detail templates to reflect canonical status and improved synonym display.
- Implemented migration scripts to establish canonical relationships based on existing synonym links.

atlas/migrations/0086_add_canonical.py

@@ -0,0 +1,69 @@
+from django.db import migrations, models
+
+
+def forwards(apps, schema_editor):
+    Condition = apps.get_model("atlas", "Condition")
+    # Build connected components using existing M2M 'synonym' links
+    visited = set()
+
+    for cond in Condition.objects.all():
+        if cond.pk in visited:
+            continue
+        # BFS/DFS to collect component
+        stack = [cond]
+        comp = []
+        while stack:
+            c = stack.pop()
+            if c.pk in visited:
+                continue
+            visited.add(c.pk)
+            comp.append(c)
+            # access existing M2M relations
+            for s in c.synonym.all():
+                if s.pk not in visited:
+                    stack.append(s)
+
+        # choose canonical: prefer primary==True else lowest pk
+        canon = None
+        for c in comp:
+            if getattr(c, "primary", False):
+                canon = c
+                break
+        if not canon:
+            canon = min(comp, key=lambda x: x.pk)
+
+        # set canonical for all non-canonical members
+        for c in comp:
+            if c.pk != canon.pk:
+                c.canonical_id = canon.pk
+                c.save()
+
+
+def backwards(apps, schema_editor):
+    Condition = apps.get_model("atlas", "Condition")
+    for c in Condition.objects.all():
+        if c.canonical_id:
+            c.canonical_id = None
+            c.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("atlas", "0085_rename_case_detail_caseprior_casedetail_and_more"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="condition",
+            name="canonical",
+            field=models.ForeignKey(
+                related_name="aliases",
+                null=True,
+                on_delete=models.SET_NULL,
+                to="atlas.condition",
+                blank=True,
+            ),
+        ),
+        migrations.RunPython(forwards, backwards),
+    ]