Do include content type on status API model actually

This is mostly important when deleting and redrafting.

The comment on `apimodel.Status.Text` implies that it's not sent except in response to status deletion, but actually this doesn't seem to be the case; it also appears to be present in responses to creations and normal fetches and stuff. So I'm treating `ContentType` the same here.

internal/api/model/status.go

@@ -110,6 +110,10 @@ type Status struct {
 	// so the user may redraft from the source text without the client having to reverse-engineer
 	// the original text from the HTML content.
 	Text string `json:"text,omitempty"`
+	// Content type that was used to parse the status's text. Returned when
+	// status is deleted, so if the user is redrafting the message the client
+	// can default to the same content type.
+	ContentType StatusContentType `json:"content_type,omitempty"`
 	// A list of filters that matched this status and why they matched, if there are any such filters.
 	Filtered []FilterResult `json:"filtered,omitempty"`
 	// The interaction policy for this status, as set by the status author.

internal/typeutils/internaltofrontend.go

@@ -1391,6 +1391,7 @@ func (c *Converter) baseStatusToFrontend(
 		Emojis:             apiEmojis,
 		Card:               nil, // TODO: implement cards
 		Text:               s.Text,
+		ContentType:        c.ContentTypeToAPIContentType(ctx, s.ContentType),
 		InteractionPolicy:  *apiInteractionPolicy,
 	}