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__newInvoiceId.sql

@@ -0,0 +1,19 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__newInvoiceId]
+(
+	@year int
+)
+RETURNS varchar(25)
+AS
+BEGIN
+	DECLARE @lastid_int bigint;
+	SELECT @lastid_int = MAX(  TRY_PARSE(RIGHT([InvoiceId], 4) as integer) ) FROM [dbo].[fds__invoices] WHERE LEFT(ISNULL([InvoiceId],''),5) = ('R' + CAST(@year as varchar(4)));
+	DECLARE @invoice_id varchar(25) = 'R' + CAST(@year as varchar(4)) + '-' + FORMAT(ISNULL(  @lastid_int , CASE WHEN @year = 2021 THEN 1593 ELSE 0 END) + 1, '0000');
+
+	RETURN @invoice_id;
+
+END