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/ott_b26.sql

@@ -0,0 +1,38 @@
+-- =============================================
+-- Author:		<Author,,Name>
+-- Create date: <Create Date, ,>
+-- Description:	<Description, ,>
+-- =============================================
+CREATE FUNCTION [dbo].[ott_b26]
+(
+	@number int
+)
+RETURNS varchar(10)
+AS
+BEGIN
+	DECLARE @RET varchar(10)
+
+	/*
+		SELECT
+		   *,
+		   LetterCode =
+			  Coalesce((SELECT Char(65 + (N.Num - 475255) / 456976 % 26) WHERE N.Num >= 475255), '')
+			  + Coalesce((SELECT Char(65 + (N.Num - 18279) / 17576 % 26) WHERE N.Num >= 18279), '')
+			  + Coalesce((SELECT Char(65 + (N.Num - 703) / 676 % 26) WHERE N.Num >= 703), '')
+			  + Coalesce((SELECT Char(65 + (N.Num - 27) / 26 % 26) WHERE N.Num >= 27), '')
+			  + (SELECT Char(65 + (N.Num - 1) % 26))
+		FROM (VALUES(18931)) as N(Num)
+		ORDER BY N.Num
+	*/
+
+	SET @RET = LOWER(
+			  Coalesce((SELECT Char(65 + (@number - 475255) / 456976 % 26) WHERE @number >= 475255), '')
+			  + Coalesce((SELECT Char(65 + (@number - 18279) / 17576 % 26) WHERE @number >= 18279), '')
+			  + Coalesce((SELECT Char(65 + (@number - 703) / 676 % 26) WHERE @number >= 703), '')
+			  + Coalesce((SELECT Char(65 + (@number - 27) / 26 % 26) WHERE @number >= 27), '')
+			  + (SELECT Char(65 + (@number - 1) % 26))
+			  );
+	
+	RETURN @RET;
+
+END