rework internal order system

backend/src/database/migrations/049_add_parent_id_to_kategorien.sql

@@ -0,0 +1,13 @@
+-- Migration 049: Add parent_id to categories for subcategory support
+-- (048 already created the table without parent_id)
+
+ALTER TABLE ausruestung_kategorien_katalog
+  ADD COLUMN IF NOT EXISTS parent_id INT REFERENCES ausruestung_kategorien_katalog(id) ON DELETE CASCADE;
+
+-- Unique: top-level categories by name
+CREATE UNIQUE INDEX IF NOT EXISTS ausruestung_kat_top_unique
+  ON ausruestung_kategorien_katalog (name) WHERE parent_id IS NULL;
+
+-- Unique: subcategories by (parent_id, name)
+CREATE UNIQUE INDEX IF NOT EXISTS ausruestung_kat_child_unique
+  ON ausruestung_kategorien_katalog (parent_id, name) WHERE parent_id IS NOT NULL;