fix: update seed files to use mgmt schema after migration

The search_path was changed from kanzlai to mgmt but seed files
still referenced the old schema. Also added missing is_spawn and
spawn_label columns to mgmt.deadline_rules via direct DB migration.

Root cause of timeline 404 / calculate+determine 400: the ruleColumns
query selected is_spawn and spawn_label which didn't exist in the
mgmt.deadline_rules table, causing all deadline rule queries to fail.

backend/seed/demo_data.sql

@@ -2,7 +2,7 @@
 -- Creates 1 test tenant, 5 cases with deadlines and appointments
 -- Run with: psql $DATABASE_URL -f demo_data.sql
 
-SET search_path TO kanzlai, public;
+SET search_path TO mgmt, public;
 
 -- Demo tenant
 INSERT INTO tenants (id, name, slug, settings) VALUES

backend/seed/seed_upc_timeline.sql

@@ -1,6 +1,6 @@
 -- UPC Proceeding Timeline: Full event tree with conditional deadlines
 -- Ported from youpc.org migrations 039 + 040
--- Run against kanzlai schema in flexsiebels Supabase instance
+-- Run against mgmt schema in youpc.org Supabase instance
 
 -- ========================================
 -- 1. Add is_spawn + spawn_label columns