…ay inside on mobile (#518)

PR #513 added CopyableValue (`min-w-0 flex-1 overflow-x-auto` on the value
span) so long SSH commands and API keys would scroll inside the row instead
of pushing siblings. The fix works in isolation but the row itself still
escapes its dialog on narrow viewports — reproducer is the Sandboxes "Create
SSH Access" dialog, where the ssh command renders past the right edge of
AlertDialogContent.

Root cause: `AlertDialogContent` uses `display: grid` with no explicit
`grid-template-columns`, so it gets a single implicit auto column whose
items default to `min-width: auto` (= min-content). With `whitespace-nowrap`
on the CopyableValue value span, that min-content is the full unbreakable
SSH command, so the grid item grows past `max-w-[calc(100%-2rem)]` and
visually clips at the viewport. `DialogContent` has the same shape with
`flex flex-col` items (which also default to `min-width: auto` on the cross
axis).

Fix:
- AlertDialogContent: add `grid-cols-[minmax(0,1fr)]` so the single column
  is `minmax(0,1fr)` instead of implicit auto. Items can now shrink below
  content width, and CopyableValue's internal `overflow-x-auto` engages.
- DialogContent: add `[&>*]:min-w-0` so every direct flex-col child gets
  `min-width: 0`. Same effect: children can shrink, content scrolls inside
  the row.

Fixes every existing CopyableValue + future long-content cases in one place
instead of patching every call site.