In Fiori app, use bookstore consistently

This also fixes validation errors from annotation LSP, which missed some
of the bookstore elements

Signed-off-by: Christian Georgi <christian.georgi@sap.com>

bookstore/index.cds

@@ -0,0 +1,4 @@
+namespace sap.capire.bookshop; //> important for reflection
+
+using from '@capire/bookshop';
+using from './db/schema';