chore(db): back up email templates before redesign

Store the original template subjects and bodies as restore scripts so the redesigned notifications can be reverted against DD_ECM if needed.

EnvelopeGenerator.Server/EmailTemplateBackups/DocumentSigned_original.sql

@@ -0,0 +1,14 @@
+-- Original email template: DocumentSigned (GUID 3)
+-- Backed up before redesign: 2026-10-29 16:25:45
+-- Subject: Dokument [RECEIVER_ACTION]: ''[DOCUMENT_TITLE]''
+-- Restore by running this script against DD_ECM:
+UPDATE dbo.TBSIG_EMAIL_TEMPLATE
+SET BODY = N'Guten Tag [NAME_RECEIVER],<br />
+<br />
+hiermit bestätigen wir Ihnen die erfolgreiche [FINAL_STATUS] für den Vorgang <B><I>''[DOCUMENT_TITLE]''</I></B>.<br />
+Wenn alle [FINAL_ACTION] haben, erhalten Sie ebenfalls per E-Mail ein abgeschlossenes Exemplar mit entsprechendem Zertifikat!
+<br />
+Mit freundlichen Grüßen<br />
+<br />
+[NAME_PORTAL]'
+WHERE GUID = 3;