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/Tables/fis_widgets_cache.sql

@@ -0,0 +1,8 @@
+CREATE TABLE [dbo].[fis_widgets_cache] (
+    [account]     VARCHAR (50)   NOT NULL,
+    [short_name]  VARCHAR (50)   NOT NULL,
+    [person_guid] VARCHAR (36)   NULL,
+    [date]        DATE           NOT NULL,
+    [data]        NVARCHAR (MAX) NOT NULL
+);
+