Allow editing link title

When using a link as a title, deck helpfully fetches the page's title and show it instead of the bare url.
But for some pages this title will be meaningless, for example pages behind a login-wall.

It would be nice to allow editing the title that is shown, while still keeping all the conveniences of having a link as a title. Such as clickable links in the overview.

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The issue names no files, tests, or entry points. Start by locating how link titles are fetched, stored, and displayed in the card editor and overview; then determine how an edited title can remain a clickable link. Done means users can override a fetched page title while preserving the existing link behavior.