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/views.py

@@ -868,14 +868,31 @@ def condition_detail(request, pk):
         if not other and synonym_name:
             other, created = Condition.objects.get_or_create(name=synonym_name)
             if created:
-                # mark created synonym as non-primary
-                other.primary = False
-                other.save()
+                # created condition: treat as alias by setting canonical below
+                pass
 
         if other and other != condition:
-            # add mutual synonym relationship
-            condition.synonym.add(other)
-            other.synonym.add(condition)
+            # Option B: treat synonym as alias/canonical relationship.
+            # Determine canonical/master for the current condition
+            master = condition.canonical if condition.canonical else condition
+
+            # If `other` belongs to a different canonical group, move its group
+            # to point at our master. If `other` has no canonical, set it.
+            if other.canonical:
+                # move the whole other group (canonical + aliases) to our master
+                    group_master = other.canonical
+                    members = Condition.objects.filter(Q(canonical=group_master) | Q(pk=group_master.pk))
+                    for m in members:
+                        if m.pk != master.pk:
+                            m.canonical = master
+                            m.save()
+            else:
+                # other is standalone; make it an alias of our master
+                other.canonical = master
+                other.save()
+
+            # Master is indicated by having no `canonical` pointer. Ensure
+            # it remains canonical (no save required unless changed elsewhere).
 
         # If this was an HTMX request return the updated synonyms partial so the
         # page can be updated without a full redirect. Otherwise perform the