feat: remove the 10,000-character article body limit and make the New article body optional

docs/design/screens/new-article.md

@@ -20,6 +20,6 @@ Recommendation: a modal. Title is the only field. The body is not asked for here
 |---|---|---|---|
 | 1 | Default | "New article" from Home, Articles or the empty state. |  |
 | 2 | Validation | On submit or blur. Nothing is sent. | "Use at least 3 characters." |
-| 3 | Submitting | Request in flight. Fields are disabled and the dialog can't be dismissed. | "Creating…" / "Choosing tiles for a small bathroom" / "Small rooms show every grout line, so we start with the floor." |
-| 4 | Title rejected (400) | A server 400 that got past the browser checks. The raw error isn't shown. | "Something in the form isn't valid. Check the highlighted fields." / "Choosing tiles for a small bathroom" / "Small rooms show every grout line, so we start with the floor." / "Check this title and try again." |
-| 5 | Error | 500 or network failure. | "Couldn't create the article. Your text is still here. Try again in a moment." / "Choosing tiles for a small bathroom" / "Small rooms show every grout line, so we start with the floor." |
+| 3 | Submitting | Request in flight. Fields are disabled and the dialog can't be dismissed. | "Creating…" / "Choosing tiles for a small bathroom" |
+| 4 | Title rejected (400) | A server 400 that got past the browser checks. The raw error isn't shown. | "Something in the form isn't valid. Check the highlighted fields." / "Choosing tiles for a small bathroom" / "Check this title and try again." |
+| 5 | Error | 500 or network failure. | "Couldn't create the article. Your text is still here. Try again in a moment." / "Choosing tiles for a small bathroom" |