When a Flow topic is listed on a category page, we should use the title of the topic as the sort key, rather than the UUID.

Example:

James H created a topic named "I request this article!" -- Topic:Sej3daex9w9p6zu0 on Wikipedia talk:Flow/Developer test page .

James says:
I sorted this topic into Category:WikiProject X as a test and so I could keep track of this particular topic. In the category listing the topic rightfully displays as "I request this article! on Wikipedia talk:Flow/Developer test page," but it is sorted under "S." The topic name begins with "I," the board name begins with either "W" or "F" (depending on whether the namespace counts), which can only mean it is sorted under "S" for "Sej3daex9w9p6zu0." Would it be possible to use the topic display name as the sort key, in the absence of another defined sort key?

And any defined sort key: Category:Foo|* Category:Foo|A