rework internal order system

backend/src/database/migrations/048_katalog_eigenschaften.sql

@@ -1,17 +1,23 @@
 -- Migration 048: Catalog categories table + item characteristics
--- - Admin-managed categories (replacing free-text kategorie)
+-- - Admin-managed categories with subcategories (replacing free-text kategorie)
 -- - Per-item characteristics (options or free-text)
 -- - Characteristic values per request position
 -- - Remove view_all permission (approve covers it)
 -- - Add manage_categories permission
 
--- 1. Categories table
+-- 1. Categories table (with parent_id for subcategories)
 CREATE TABLE IF NOT EXISTS ausruestung_kategorien_katalog (
-  id    SERIAL PRIMARY KEY,
-  name  TEXT NOT NULL UNIQUE,
-  erstellt_am TIMESTAMPTZ DEFAULT NOW()
+  id         SERIAL PRIMARY KEY,
+  name       TEXT NOT NULL,
+  parent_id  INT REFERENCES ausruestung_kategorien_katalog(id) ON DELETE CASCADE,
+  erstellt_am TIMESTAMPTZ DEFAULT NOW(),
+  UNIQUE(name, parent_id)
 );
 
+-- Add unique constraint for top-level categories (parent_id IS NULL)
+CREATE UNIQUE INDEX IF NOT EXISTS ausruestung_kategorien_top_level_unique
+  ON ausruestung_kategorien_katalog (name) WHERE parent_id IS NULL;
+
 -- Migrate existing categories from free-text
 INSERT INTO ausruestung_kategorien_katalog (name)
 SELECT DISTINCT kategorie FROM ausruestung_artikel WHERE kategorie IS NOT NULL AND kategorie != ''
@@ -24,7 +30,7 @@ ALTER TABLE ausruestung_artikel ADD COLUMN IF NOT EXISTS kategorie_id INT REFERE
 UPDATE ausruestung_artikel a
 SET kategorie_id = k.id
 FROM ausruestung_kategorien_katalog k
-WHERE k.name = a.kategorie AND a.kategorie_id IS NULL;
+WHERE k.name = a.kategorie AND a.kategorie_id IS NULL AND k.parent_id IS NULL;
 
 -- 2. Characteristics definitions per catalog item
 CREATE TABLE IF NOT EXISTS ausruestung_artikel_eigenschaften (