Render settings from the device-reported schema

[chrispmonkey]

Renders the settings form from the device's GET /api/settings/schema descriptor
instead of hardcoding each field in SettingsPage.tsx. A new setting the device
adds shows up here with no client change.

The descriptor is sections of typed fields (string / text / secret / bool
/ enum); SchemaSettingsForm maps each type to a control, visibleWhen gates
conditional fields, and secret fields stay write-only (the device reports only
configured, so a save sends just what changed). Falls back to the existing
fixed form when the device doesn't serve the descriptor.

Pairs with the server side (PenumbraOS/humane-system-hook#10), which emits the
descriptor.

[chrispmonkey]

Updated to write through the existing typed PUT /api/settings (nesting the descriptor's flat keys), pairing with the now read-only descriptor endpoint in PenumbraOS/humane-system-hook#10.