todo_widget: Allow task list title to be set and edited by author.

Users can now name task lists by providing the task list title in the
`/todo` command on the same line. Example: `/todo School Work`. If no
title is provided by the user, "Task list" (which is also the
placeholder) is used as default.

The author of a task list can later edit / update the task list title
in the todo widget, just like the question in the poll widget.

Fixes part of #20213.

web/src/submessage.ts

@@ -29,12 +29,21 @@ const poll_widget_extra_data_schema = z
     })
     .nullable();
 
+export const todo_widget_extra_data_schema = z
+    .object({
+        task_list_title: z.string().optional(),
+    })
+    .nullable();
+
 const widget_data_event_schema = z.object({
     sender_id: z.number(),
     data: z.discriminatedUnion("widget_type", [
         z.object({widget_type: z.literal("poll"), extra_data: poll_widget_extra_data_schema}),
         z.object({widget_type: z.literal("zform"), extra_data: zform_widget_extra_data_schema}),
-        z.object({widget_type: z.literal("todo"), extra_data: z.null()}),
+        z.object({
+            widget_type: z.literal("todo"),
+            extra_data: todo_widget_extra_data_schema,
+        }),
     ]),
 });