Clean up changelog format

[mariojg-dev]

There are multiple new releases everyday and the format the changelog is written right now makes a bit hard to follow everything has changed after an update. Would be great to get the changelog in a more readable format, like bullet points with a more concise description about the change. Thanks for the work! :)

[ulsklyc]

Thanks - and you are right about the symptom, so let me tell you what I did with it and what I did not.

The part I am keeping is the prose. This changelog says why something was decided the way it was, and for a one-person project that is often the only place it is written down. Six months from now, "why does the OpenWeatherMap branch bundle by local day" has an answer here and nowhere else. Cut down to bullet points, that is gone.

The part you are right about is that finding what changed should not cost three paragraphs.

Both fit, and the fix is small: every entry now opens with a bolded sentence naming the change, with the reasoning underneath.

### Fixed
- **The weather forecast was off by a day** (#851). The server already keeps the
  running day out of `forecast` so it is not shown twice - but the display kept
  labelling `forecast[0]` "Today" ...

Scan the bold lines and you have the release. Stop at any of them and you get the story.

What surprised me while checking: it is nearly the practice already. Across the last six releases, 23 of 28 entries carried a lead-in like that. What was missing was the rule - which is exactly why it did not help you: a format you cannot rely on is not a format, it is a coincidence.

So it is a rule now, with a test behind it (#854), for [Unreleased] and every version from 2.41.0 on. Not retroactively: 1740 of 2551 entries predate the habit, and a published changelog does not get rewritten.

One thing I did not do, and would rather hear from you first: the GitHub release notes are the same text. If what you actually read after an update is the release page rather than the file, a short bullet summary at the top of the notes might serve you better than anything I can do inside the changelog. Say the word if that is where you are looking.

[ulsklyc]

@mariojg-dev A late note, because your request turned out to carry more than the changelog file.

The rule you asked for - every entry opening with a bolded sentence that names the change - is what the app now reads. The changelog view opens with a "New in your app" list built from exactly those lead sentences, each expandable for the reasoning underneath, and it answers a different complaint (#496: releases arriving faster than people can follow). Without your format there would have been nothing to scan; the view would have had to invent a second, shorter text per release, in 24 languages, at several releases a day.

So the small formatting fix from August is doing work nobody planned for it. Thank you for pushing on it.