v2.6.1

One invitation to reply, and the same one wherever a reply can be written
(MR !203).

- A post offered two ways into the same editor: the footer's reply arrow and
  the box that says "post your reply", a few pixels apart. The box wins while
  it is on offer, because it is the one that says what it does, and the arrow
  comes back once the editor is open, where it is no longer a duplicate but the
  way to close it again. Both controls now read one exported, pure rule instead
  of each testing its own conditions, and a sweep of every combination asserts
  they are never on screen together -- testing each condition separately is
  exactly how they drifted into overlapping.

- With the arrow hidden, a post whose reader can do nothing else to it, neither
  the author nor a moderator, still got the footer's action tab drawn around
  nothing. The footer decides by whether it was handed actions, and a JSX
  element is truthy however little it renders, so it cannot work this out for
  itself. It is told instead.

- A reply card offered an arrow where the post above it offers a box: the same
  action presented as two different things to learn. The invitation now lives in
  a component of its own, with its own stylesheet, so the post and the card
  cannot drift apart, and the rule that keeps the arrow and the box from both
  appearing travels beside it. Only where an inline reply is actually on offer,
  which is the replies tab and nowhere else; a feed card is untouched.

- The block holding the invitation carried no `order` inside `.articles__content`,
  a flex row whose children are ordered explicitly on a scale that differs by
  breakpoint. Taking 0, it sorted ahead of the footer and shrank into a flex item
  beside the body, so the box floated mid-card with empty space around it. Past
  the largest footer order at full basis, it lands under the footer at every
  width.

- On a card the invitation takes the step and the dotted rule the threaded view
  already uses for a nested reply: 62px in, collapsing to 10px on a phone the
  way comments do, and stopping at 34rem so a wide screen gives it air rather
  than more box.