Add Fuchs_Database SSDT project (schema source of truth)

Adds the SQL Server Data Tools project for the fuchs_fds database — tables,
table types, functions and stored procedures that the backend calls (e.g.
fds__getInvoice, fds__merge_bankingtransactions, fds__tt__bankingtransactions,
fds__admin_getReportCatalog, fis_* auth). Build/model caches (bin, obj,
*.dbmdl, *.jfm, *.user) are git-ignored.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Fuchs_Database/dbo/Functions/vat_val.sql

@@ -0,0 +1,22 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[vat_val]
+(
+	@price numeric(10,3)
+	,@quantityhours numeric(10,3)
+	,@discount numeric(10,3)
+	,@VAT numeric(10,3)
+)
+RETURNS numeric(7,2)
+AS
+BEGIN
+	DECLARE @Ret numeric(7,2)
+
+	SET @RET = [dbo].[net_val](@price, @quantityhours, @discount) * ((ISNULL(@vat, 19.0) * 0.01));
+
+	RETURN @RET;
+
+END