mara's follow-up: both cards should be the same size (flex: 1 1 0
instead of the form keeping its own narrower basis), and the form's
inputs should fill the card rather than stopping at their old 16em
cap. Dropped that cap from the shared form kit (.ui-form-control /
.ui-form-field) entirely rather than overriding it per-page — the kit
itself has no width opinion now, same as Panel already has none; a
page that wants a narrower field caps its layout, not the kit.
Checked ComponentsPage's standalone samples (no regression, just
wider) and narrow-viewport stacking (still moves the explanation
under the form).
TextField and SelectField's shared FormField wrapper had no width of
its own, so inside the form's shrink-to-fit flex column each field's
input/select resolved its 'width: 100%' against its own shrunk
wrapper rather than a shared column width — two fields with
differently-long labels ended up with differently-wide controls.
FormField now caps its own width the same way the control already
does, so every field in a form lines up regardless of label length.
Also wrapped the page in a max-width container: Panel has no width
opinion of its own, so it filled the full page column, leaving a lot
of bare panel to the right of the ~16em-wide form.
Closes#3448.
New ui/ primitives: FormField (shared label+control wrapper),
TextField, SelectField, Button — each with a min-height touch target
(2.75em ~= 44px, WCAG 2.5.5) per mara's #3447 ask, and a max-width
instead of a fixed width so the control caps on desktop without
overflowing a narrow/touch viewport.
CreateAgentPage's name field + submit button now come from the kit
instead of page-scoped CSS; ComponentsPage gets a section for each new
primitive with an editable sample.
