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__r_getBalanceThisMonth.sql

@@ -0,0 +1,33 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date,,>
+-- Description:	<Description,,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__r_getBalanceThisMonth](
+	@authuser varchar(100)
+)
+RETURNS varchar(25)
+BEGIN
+	DECLARE @today date = GETDATE();
+	DECLARE @tomorrow date = DATEADD(DAY,1,@today);
+	DECLARE @thismonthfirst date = [dbo].[date_monthfirst](@today);
+	DECLARE @ret varchar(25) = ''
+
+	IF [dbo].[fis_getModuleAuth]('fds_reports', @authuser) < 2
+		SET @ret = '';
+	ELSE 
+		BEGIN
+		
+			WITH inv as (
+				SELECT 
+						[Dateofcreation] = i.[DateFinalized]
+						,i.[InvoiceBalance]
+						,[InvoiceBalanceNetto] = i.[InvoiceBalance_net]
+					FROM [dbo].[fds__invoices] as i 
+					WHERE i.[isFinal] = 1 AND [dbo].[date_monthfirst](i.[DateFinalized]) = @thismonthfirst
+			)
+			SELECT TOP(1) @ret = FORMAT(  SUM(  ISNULL(inv.[InvoiceBalanceNetto],0) ) * 0.001, '#,0 k€', 'de') FROM inv;
+		END
+
+	RETURN @ret;
+END