Add forced migration for semester deadline updates

This migration will automatically run during deployment and update
all existing quarterly confirmation deadlines to the new semester-based system:
- Q1: March 15 (Spring semester primary submission)
- Q2: June 15 (auto-approved when Q1 approved)
- Q3: September 15 (Fall semester primary submission)
- Q4: December 15 (auto-approved when Q3 approved)

No manual intervention required on VPS - GitHub Action will deploy and migrate automatically.

app/stiftung/migrations/0036_force_semester_deadlines_update.py

@@ -0,0 +1,13 @@
+# Generated by Django 5.0.6 on 2025-09-30 19:45
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stiftung', '0035_update_semester_deadlines'),
+    ]
+
+    operations = [
+    ]