docs(todo): add synopsis and examples to todo commands
Description
Adds Long (Synopsis) fields to the todo command and its 2 subcommands,
as part of the style guide audit identified in #8263 (closed).
Each Synopsis explains the command's default behavior and key flags — how
to-do items are collected, how to filter the list with --state,
--action, and --type, and how to mark items done individually or with
--all. The Synopsis text is additive and does not repeat the Short
description.
Commands updated:
todotodo donetodo list
Content follows the documentation style guide and the GitLab CLI (glab) documentation style guide.
Related issues and merge requests
Documentation
If this MR adds or updates CLI command documentation, follow the conventions in the
GitLab CLI (glab) documentation style guide,
run make gen-docs, and commit the updated files in docs/source/.