feat(leads): link consumer account to lead on submission

- user_account FK on Lead model (SET_NULL, related_name='submitted_leads')
- Migration 0004_lead_user_account
- ScheduleCallView auto-matches consumer account by email on create
- _serialize_lead now returns userAccount: {id, name, email, phone, eventifyId, profilePicture}

admin_api/migrations/0004_lead_user_account.py

@@ -0,0 +1,28 @@
+# Generated by Django 4.2.21 on 2026-04-07
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('admin_api', '0003_lead'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='lead',
+            name='user_account',
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name='submitted_leads',
+                to=settings.AUTH_USER_MODEL,
+                help_text='Consumer platform account that submitted this lead (auto-matched by email)',
+            ),
+        ),
+    ]