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_IntermediateIsAllocatedToOther.sql

@@ -0,0 +1,22 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__fn_IntermediateIsAllocatedToOther]
+(
+	@Intermediate_InvID varchar(10)
+	,@Target_InvID varchar(10)
+
+)
+RETURNS bit
+AS
+BEGIN
+	DECLARE @IsA bit = CASE WHEN EXISTS (SELECT * FROM [dbo].[fds__invoices] as intermediates JOIN [dbo].[fds__invoice_details] as id on intermediates.[Id] = id.[InvId] and id.[AllocatedTo_InvId] is not null
+														JOIN [dbo].[fds__invoices] as non_intermediates ON id.[AllocatedTo_InvId] = non_intermediates.[Id] and id.[AllocatedTo_InvId] is not null
+													WHERE intermediates.[Id] = @Intermediate_InvID and (@Target_InvID is null or non_intermediates.[Id] <> @Target_InvID))
+									THEN 1 ELSE 0 END;
+
+	RETURN @isA;
+
+END