Brains roster and Machines strip: phone-width polish

Found while screenshotting Directory > Machines > Brains at 360px (Task 6593): 1. At 360px a Brains row's account name wraps onto three lines and its "no credentials" chip is clipped mid-word ("no creden"); keep the name to one line (ellipsis) and let the chip drop below or shrink so it reads whole. 2. At 360px the Machines strip puts "Brains" alone on a second line under Nodes…NodeLink; scroll the strip horizontally or shorten it so every tab sits on one line, as other strips do. 3. At 360px the Share subscriptions dialog's footer stacks Create on its own row under "Missing… / Cancel"; keep Cancel and Create side by side and let the missing-fields line wrap above them. 4. On the AWS credential form (/credentials/new?type=aws) the Region field is not visible without opening a fold, although Share subscriptions and Connections read it; show it in the first view or name it in the fold's label. Out of scope: server behaviour; desktop layout of the Brains roster (capped at 960px by Task 6593). Done means: each item changed or declined with a one-line reason in the PR body, with a 360px screenshot per changed surface; `./dc check full` green.

All 4 phone-width items changed (Brains row name/chip, Machines strip scrolls, Share dialog footer, AWS Region outright); 360px visual check done, all read cleanly. Full gate green; PR #5609 merged, Jaah Deploy succeeded. Follow-up draft #6685.