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/date_nextFirst.sql

@@ -0,0 +1,29 @@
+
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[date_nextFirst]
+(
+	@date date
+	,@unit varchar(1)
+)
+RETURNS date
+AS
+BEGIN
+	DECLARE @ret date;
+	SET @unit = LOWER(ISNULL(@unit, ''));
+
+	SET @ret = CASE 
+				WHEN @unit = 'y' THEN DATEADD(YEAR, 1, DATEFROMPARTS(YEAR(@date), 1,1))
+				WHEN @unit = 'q' THEN DATEADD(MONTH, 4 - Month(@date) % 3, DATEFROMPARTS(YEAR(@date),MONTH(@date),1))
+				WHEN @unit = 'm' THEN DATEADD(MONTH, 1, DATEFROMPARTS(YEAR(@date), MONTH(@date),1))
+				WHEN @unit = 'w' THEN DATEADD(WEEK, 1, [dbo].[date_weekfirst](@date))
+				WHEN @unit = 'd' THEN DATEADD(DAY, 1, @date)
+				ELSE NULL
+				END;
+
+	RETURN @ret
+
+END