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/fds__admin_activity.sql

@@ -0,0 +1,9 @@
+CREATE TABLE [dbo].[fds__admin_activity] (
+    [uid]       BIGINT         IDENTITY (1, 1) NOT NULL,
+    [timestamp] DATETIME       CONSTRAINT [DF_fds__admin_activity_timestamp] DEFAULT (getutcdate()) NOT NULL,
+    [activity]  VARCHAR (50)   NOT NULL,
+    [authuser]  VARCHAR (10)   NULL,
+    [info]      VARCHAR (1000) NULL,
+    [data]      NVARCHAR (MAX) NULL
+);
+