feat(admin): LicServer config manageable via admin settings UI

- Migration: add licserver_base_url/api_key cols to settings table
- New: lib/actions/licserver-config.ts (read/write/test server actions)
- Updated: proxy routes read config from DB with env-var fallback
- Updated: admin/einstellungen adds LicServer card with URL + API key
  input, show/hide toggle, Save and Connection Test buttons

shop/supabase/migrations/20260714000000_add_licserver_config_to_settings.sql

@@ -0,0 +1,11 @@
+-- Migration: Add LicServer configuration columns to settings table
+ALTER TABLE public.settings
+  ADD COLUMN IF NOT EXISTS licserver_base_url TEXT,
+  ADD COLUMN IF NOT EXISTS licserver_api_key  TEXT;
+
+-- Ensure the licserver config row exists (upsert with empty defaults)
+INSERT INTO public.settings (id, licserver_base_url, licserver_api_key)
+VALUES ('licserver', NULL, NULL)
+ON CONFLICT (id) DO NOTHING;
+
+NOTIFY pgrst, 'reload schema';