fix: disabling last store/group no longer resets all to enabled

Added store_filters_seeded / group_filters_seeded flags to SyncConfig.
_enabled_*_ids now returns None (all enabled) only before first toggle,
not when the filter table is empty due to all being disabled.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/migrations/versions/0011_sync_config_filter_seeded_flags.py

@@ -0,0 +1,36 @@
+"""Add store_filters_seeded and group_filters_seeded to sync_configs."""
+revision = "0011"
+down_revision = "0010"
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    op.add_column("sync_configs", sa.Column("store_filters_seeded", sa.Boolean(), nullable=False, server_default="0"))
+    op.add_column("sync_configs", sa.Column("group_filters_seeded", sa.Boolean(), nullable=False, server_default="0"))
+
+    # Mark existing rows as seeded if they already have filters
+    op.execute("""
+        UPDATE sync_configs sc
+        SET store_filters_seeded = 1
+        WHERE EXISTS (
+            SELECT 1 FROM sync_filters sf
+            WHERE sf.sync_config_id = sc.id AND sf.entity_type = 'store'
+        )
+    """)
+    op.execute("""
+        UPDATE sync_configs sc
+        SET group_filters_seeded = 1
+        WHERE EXISTS (
+            SELECT 1 FROM sync_filters sf
+            WHERE sf.sync_config_id = sc.id AND sf.entity_type = 'group'
+        )
+    """)
+
+
+def downgrade():
+    op.drop_column("sync_configs", "group_filters_seeded")
+    op.drop_column("sync_configs", "store_filters_seeded")