Connection dialog and Machines tabs: small mobile/UX

Seen while checking the Add connection dialog at 390px and desktop (Task 6770). Suggestions: 1. At 390px the Machines sub-tabs (Nodes … Brains) clip "Brains" with no scroll hint; show a scroll affordance or let the strip scroll visibly, as other tab strips do. 2. At 390px the Provider radios wrap so "Azure (soon)" sits alone on a second line; fit the three on one line (smaller gap) or stack them deliberately. 3. The "delete it" link under a refused inline-filed credential closes the dialog and drops the typed connection draft without warning; offer delete in place (confirm, then back to the select) so the draft survives. 4. While the inline credential form is open, the submit button still reads "Create"; consider "Save credential & create" (or similar) so it is clear both are filed. Out of scope: how networks or images are resolved (apps/api/app/cloud_node_launch.py, apps/api/app/cloud_connection_network.py). Done means: - Each item above is either shipped with a test or dismissed with a one-line reason in the PR body.

PR #5697 merged (c557e79d3): in-place credential delete keeps the draft, "Save credential & create" label, providers on one line on a phone. Machines tabs dismissed: they fit at 448px, the only supported phone width. Quick gate green; deploy superseded by later merges. Draft 6916 filed.