Fix migration to check column existence before dropping (#101)

Make migration 2264546da1d9 idempotent by checking if columns exist
before attempting to drop them. This prevents failures when columns
don't exist, fixing the Init:CrashLoopBackOff issue in Kubernetes
deployments.

Author: geeth24

server/alembic/versions/2264546da1d9_simplify_alert_preferences.py

@@ -20,13 +20,18 @@
 
 def upgrade() -> None:
     """Upgrade schema."""
-    # ### commands auto generated by Alembic - please adjust! ###
-    with op.batch_alter_table('user_alert_preferences', schema=None) as batch_op:
-        batch_op.drop_column('alert_types')
-        batch_op.drop_column('email_min_severity')
-        batch_op.drop_column('disaster_types')
+    # Check if columns exist before dropping them (idempotent migration)
+    conn = op.get_bind()
+    inspector = sa.inspect(conn)
+    columns = [col["name"] for col in inspector.get_columns("user_alert_preferences")]
 
-    # ### end Alembic commands ###
+    with op.batch_alter_table('user_alert_preferences', schema=None) as batch_op:
+        if "alert_types" in columns:
+            batch_op.drop_column("alert_types")
+        if "email_min_severity" in columns:
+            batch_op.drop_column("email_min_severity")
+        if "disaster_types" in columns:
+            batch_op.drop_column("disaster_types")
 
 
 def downgrade() -> None: