Allow SVG club logos

ImageField validates uploads through Pillow, which can't read SVGs, so
a club crest that's a vector logo was rejected outright. Switches to a
plain FileField with an extension allowlist (png/jpg/jpeg/gif/webp/svg)
instead, and restricts the file picker to image types via the widget's
accept attribute.

club/migrations/0015_alter_club_logo.py

@@ -0,0 +1,20 @@
+# Generated by Django 6.0.6 on 2026-07-24 16:40
+
+import club.models
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('club', '0014_club_secondary_color'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='club',
+            name='logo',
+            field=models.FileField(blank=True, help_text="Shown on the club's own pages. Without one, the club's initials are used.", upload_to=club.models.club_logo_path, validators=[django.core.validators.FileExtensionValidator(allowed_extensions=['png', 'jpg', 'jpeg', 'gif', 'webp', 'svg'])], verbose_name='logo'),
+        ),
+    ]