Allow project-goals to be given explicit TL;DRs, provide links by default

[nikomatsakis]

Instead of generating code with an LLM, we should adopt the following pattern

• We ask people to provide a TL;DR comment that summarizes the month. I would literally say that such a comment should be recognized because it begins with "TL;DR".
• When we ping for status updates, we look to see if a TL;DR comment has been generated. We do not ping them if it has.

When we generate the page, if there is a TL;DR comment, we include it.

At the end, we then append a link saying something like "To read the full N updates, click here." If there have been no updates, say "No updates provided this month. Click here to view the tracking issue."

[lqd]

We could also consider a short update as a TL;DR, e.g. if it has less than 280 characters or whatever.

[traviscross]

We could just take the first paragraph and tell people that we're doing this and to write in a "bottom line up front" style.

If we were to mark this somehow, I'd probably suggest "Summary: ..." instead for fluency reasons.