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_ReminderDocumentName.sql

@@ -0,0 +1,30 @@
+
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[fds__fn_ReminderDocumentName]
+(
+	@ReminderType char(1)
+	, @ReminderTitle varchar(100)
+	, @DateFinalized datetime
+	, @InvoiceId varchar(10)
+	
+)
+RETURNS varchar(50)
+AS
+BEGIN
+	DECLARE @doc varchar(50);
+
+	SET @doc = CASE WHEN @DateFinalized is null THEN ''
+					WHEN ISNULL(@ReminderTitle,'') <> '' THEN @ReminderTitle
+					WHEN @ReminderType = 'f' THEN 'Zahlungserinnerung ' + @InvoiceId
+					WHEN @ReminderType = 'c' THEN 'Mahnung ' + @InvoiceId
+					WHEN @ReminderType = 'f' THEN 'Mahnung ' + @InvoiceId
+				ELSE 'Zahlungserinnerung ' + @InvoiceId
+				END;
+
+	RETURN @doc + '.pdf';
+
+END