Let admins create and delete users in Benutzerverwaltung, modernize list

Wire up two previously-unwired stored procedures for the usr module:
- fis_admin_createUserAccount gained the missing @authaccount +
  intranet_admin auth gate, a duplicate-email check, and now returns
  the (possibly auto-generated) password so it can be emailed to the
  new user, mirroring fis_admin_resetUserPassword's pattern.
- fis_admin_delUserAccount gained the same missing auth gate plus a
  guard against an admin deleting their own account.

New /do/usr/create and /do/usr/delete endpoints in
IntranetController.AdminUsers.cs, a "Neuer Benutzer" button and a
"Benutzer löschen" ribbon action in fis.usr.js, and unit tests for the
new welcome-email content (BuildWelcomeEmail).

Also restyle the user list (fis.usr.scss) from a plain bordered table
to a card-style row grid with avatar-initial badges and status pills,
matching the Admin dashboard's visual language.

Documented as ADR 0020 and in the admin-user-management concept doc.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Fuchs_Database/dbo/Stored Procedures/fis_admin_delUserAccount.sql

@@ -12,17 +12,23 @@ AS
 BEGIN
 	SET NOCOUNT ON;
 	DECLARE @utcnow datetime = GETUTCDATE();
+	DECLARE @auth smallint = [dbo].[fis_admin_getUserAuth](@authaccount);
 
-    IF EXISTS (SELECT * FROM [dbo].[fis_useraccounts] WHERE [useraccount_id] = @useraccount_id and [DateDeleted] is null)
-		BEGIN
+	IF @auth > 1 AND @authaccount <> @useraccount_id
+	BEGIN
 
-			UPDATE [dbo].[fis_useraccounts]
-				SET [UserDeleted] = @authaccount
-				   ,[DateDeleted] = @utcnow
-			 WHERE
-				  [useraccount_id] = @useraccount_id;
+		IF EXISTS (SELECT * FROM [dbo].[fis_useraccounts] WHERE [useraccount_id] = @useraccount_id and [DateDeleted] is null)
+			BEGIN
 
-		END
+				UPDATE [dbo].[fis_useraccounts]
+					SET [UserDeleted] = @authaccount
+					   ,[DateDeleted] = @utcnow
+				 WHERE
+					  [useraccount_id] = @useraccount_id;
+
+			END
+
+	END
 
 	SELECT CAST((CASE WHEN NOT EXISTS (SELECT * FROM [dbo].[fis_useraccounts] WHERE [useraccount_id] = @useraccount_id and [DateDeleted] is null) THEN 1 ELSE 0 END) as bit);