fix(edit): treat a --when or empty notes append Things ignores as applied

[ryanlewis]

Fixes #377

An edit whose value already matches the item, such as --when someday on a Someday item, made Things record no change. edit and project edit then waited the full read-back budget and failed with "edit did not apply". This change compares those flags with the item before waiting, the same way #372 does for moves. If every flag already matches, the item prints at once with exit 0. If only some match, the edit still waits for the ones that change.

What Things does. I tested this against Things 3 on to-dos and projects and checked whether userModificationDate moved:

• No change recorded: --when anytime or an empty --when on an undated Anytime item, --when someday on an undated Someday item, --when today / evening on an item already in that part of today, today's date on either part of today, and --when tomorrow or a later date on an item already scheduled for that day. An empty --append-notes or --prepend-notes also records no change.
• Changes: an empty --when on an Inbox or Someday item (it moves to Anytime), and --when someday or anytime on a dated item.
• Reminders: --when today, evening or today's date clears a reminder, so on an item with a reminder it counts as a change. A later day keeps the reminder. The CLI didn't read reminders before, so I added HasReminder. It runs only for those values.
• --title, --notes, --tags, --add-tags and --deadline already had this check.

Flags this leaves alone. A --when with a time (18:00, date@time, RFC3339) still waits, because the CLI doesn't read the reminder time. A natural-language phrase still waits too, and so does a date already in the past.

Docs (commands.md, agents.md) and the bundled skill are updated to match.