web/settings: add the mobile user and repository settings screens
below md the sidebar collapses into a native select and the panel goes
full-bleed, keeping only its top and bottom hairlines, matching the Mobile
section of the settings redesign.
below sm the rows drop their trailing controls onto a second line: list
entries keep theirs left-aligned under the meta, while SettingsRow and the
SettingsBlock header align theirs right, as the user and repository frames
respectively do. SettingsRow takes an opt-in `stack` since the design keeps
short label/toggle pairs on one line either way.
Signed-off-by: eti <eti@eti.tf>