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__fn_unpaidInvoices.sql

@@ -0,0 +1,33 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date,,>
+-- Description:	<Description,,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__fn_unpaidInvoices]
+(	
+	
+)
+RETURNS TABLE 
+AS
+RETURN 
+(
+	WITH inv as (
+	SELECT [Id]
+				,[Invoiceid]
+				,[DateFinalized]
+				,[InvoiceBalance]
+				,[DocumentName]
+				--,[file]
+				,[InvoiceTitle]
+				,[customerid]
+				,[dateSent]
+				,[fds] = CAST(IIF(iv.isexternal = 0,1,0) as bit) 
+			FROM [dbo].[fds__invoices] as iv
+				WHERE [isfinal] = 1 
+					and CAST(CASE WHEN ISNULL(iv.[IsCanceled],0) = 1 THEN 1 ELSE ISNULL([IsPayed],0) END  as bit) = 0
+					and InvoiceBalance > 0
+					AND NOT exists (SELECT 0 FROM [dbo].[fds__invoice_details] as d where d.[StornoTo_InvId] = iv.[id])
+	)
+	SELECT *  /*[Rechnung] = [invoiceId], [Name] = [InvoiceTitle] + CHAR(10) + '  (' + (SELECT TOP(1) c.[name] FROM [dbo].[mfr__companies] as c WHERE inv.[customerid] = c.[id]) + ')', [Betrag (net)] = FORMAT([invoicebalance], '#0.00€', 'de'), [Datum] = FORMAT([DateFinalized], 'dd.MM.yy' , 'de'), [Zahlungen] = FORMAT([dbo].[fds__fn_InvoicePaymentAmount]([id]), '#0.00€', 'de'), [order] = ROW_NUMBER() OVER (ORDER BY [DateFinalized], [DateSent]) */
+	FROM inv
+)