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/fds__fn_InvoiceIdByName.sql

@@ -0,0 +1,21 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__fn_InvoiceIdByName]
+(
+	@nme varchar(255)
+)
+RETURNS varchar(20)
+AS
+BEGIN
+	DECLARE @Id varchar(20);
+
+	SET @nme = TRIM((SELECT TOP(1) [value] FROM string_split(@nme, '(')));
+
+	SET @Id = ISNULL((SELECT TOP(1) [Id] FROM [dbo].[fds__invoices] WHERE [InvoiceId] = @nme),'');
+
+	RETURN @id;
+
+END