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_addcustom.sql

@@ -0,0 +1,27 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[date_addcustom]
+(
+	@date date
+	,@phrase varchar(10)
+)
+RETURNS date
+AS
+BEGIN
+	DECLARE @returndate date, @numpart integer = TRY_PARSE(left(@phrase, patindex('%[^0-9]%', @phrase + '.') - 1) as integer), @defpart varchar(10) = LOWER(RIGHT(@phrase, LEN(@phrase) - patindex('%[^0-9]%', @phrase + '.') + 1));
+
+	SET @returndate = CASE WHEN @numpart is null then null
+						  WHEN @defpart = 'wd' THEN [dbo].[AddBusinessDays](@date, @numpart)
+						  WHEN @defpart = 'd' THEN DATEADD(DAY, @numpart, @date)
+						  WHEN @defpart = 'y' THEN DATEADD(YEAR, @numpart, @date)
+						  WHEN @defpart = 'm' THEN DATEADD(Month, @numpart, @date)
+						  WHEN @defpart = 'wk' THEN DATEADD(WEEK, @numpart, @date)
+						  ELSE @date
+					END;
+
+	RETURN @returndate;
+
+END