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/fis_admin_testGroupMembership.sql

@@ -0,0 +1,29 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[fis_admin_testGroupMembership]
+(
+	@useraccount_id varchar(5)
+	,@usergroup_id varchar(1000)
+)
+RETURNS bit
+AS
+BEGIN
+	DECLARE @groups TABLE([usergroup_id] varchar(5));
+	INSERT INTO @groups SELECT * from STRING_SPLIT(@usergroup_id,',');
+	
+	DECLARE @isMember bit = CASE WHEN EXISTS (SELECT * FROM [dbo].[fis_usergroups] as g
+														JOIN @groups as groupstotest On groupstotest.[usergroup_id] = g.[usergroup_id]
+														JOIN [dbo].[fis_usergroups_members] as gm on g.[usergroup_id] = gm.[usergroup_id] and gm.[DateDeleted] is null AND g.[DateDeleted] is null
+														JOIN [dbo].[fis_useraccounts] as u on gm.[useraccount_id] = u.[useraccount_id]
+														WHERE u.[DateDeleted] is null AND u.[DateDisabled] is null
+															and u.[useraccount_id] = @useraccount_id
+															and g.[DateDeleted] is null
+												)
+										THEN 1 ELSE 0 END;
+
+	RETURN @isMember;
+
+END