Add header_image field to PartnersPage model (#1661)

This change adds a header_image field to the PartnersPage model that can be
managed through the Wagtail admin interface. The field is exposed via the API
as header_image_url, following the same pattern as the TeamPage model.

Changes:
- Add header_image ForeignKey field to PartnersPage model
- Add get_header_image() method and header_image_url property
- Add header_image to content_panels for admin editing
- Add header_image_url to api_fields for API exposure
- Generate database migration

Jira: https://openstax.atlassian.net/browse/CORE-1194

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Co-authored-by: Michael Volo <volo@rice.edu>

Author: 3 people

pages/migrations/0164_partnerspage_header_image.py

@@ -0,0 +1,26 @@
+# Generated by Django 5.1.15 on 2026-01-13 22:51
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pages", "0163_rootpage_school"),
+        ("wagtailimages", "0027_image_description"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="partnerspage",
+            name="header_image",
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name="+",
+                to="wagtailimages.image",
+            ),
+        ),
+    ]

pages/models.py

@@ -2394,6 +2394,19 @@ class CreatorFestPage(Page):
 class PartnersPage(Page):
     heading = models.CharField(max_length=255)
     description = RichTextField()
+    header_image = models.ForeignKey(
+        'wagtailimages.Image',
+        null=True,
+        blank=True,
+        on_delete=models.SET_NULL,
+        related_name='+'
+    )
+
+    def get_header_image(self):
+        return build_image_url(self.header_image)
+
+    header_image_url = property(get_header_image)
+
     partner_landing_page_link = models.CharField(max_length=255, null=True, blank=True,
                                                  help_text="Link text to partner landing page.")
     partner_request_info_link = models.CharField(max_length=255, null=True, blank=True,
@@ -2442,6 +2455,7 @@ def partner_type_choices():
         TitleFieldPanel('title', classname='full title', help_text="Internal name for page."),
         FieldPanel('heading'),
         FieldPanel('description'),
+        FieldPanel('header_image'),
         FieldPanel('partner_landing_page_link'),
         FieldPanel('partner_request_info_link'),
         FieldPanel('partner_full_partner_heading'),
@@ -2454,6 +2468,7 @@ def partner_type_choices():
         APIField('title'),
         APIField('heading'),
         APIField('description'),
+        APIField('header_image_url'),
         APIField('partner_landing_page_link'),
         APIField('partner_request_info_link'),
         APIField('partner_full_partner_heading'),