docs(storybook): simplify Foundation Typography and Layout pages

Typography: drop the page intro, section notes, the Font Stack details and
the per-specimen source path / size list that repeated the computed summary.
Layout: drop the intro, section notes, CSS source paths, the boundary and QA
preset notes, the current preview line and the Grid / Container note.
ReferencePage intro and ReferenceSection note become optional; Color keeps its text.

src/foundation/reference.tsx

@@ -24,10 +24,10 @@ export function useResolvedProperties(properties: readonly string[]) {
 }
 
 // The page frame, title and sections are the common Story page (src/components/story-page.tsx); .hm-foundation styles the reference content.
-export function ReferencePage({ title, intro, children }: { title: string; intro: string; children: ReactNode }) {
+export function ReferencePage({ title, intro, children }: { title: string; intro?: string; children: ReactNode }) {
   return <StoryPage className="hm-foundation"><StoryPageHeader title={title} description={intro} />{children}</StoryPage>
 }
-export function ReferenceSection({ title, note, children, id }: { title: string; note: string; children: ReactNode; id?: string }) {
+export function ReferenceSection({ title, note, children, id }: { title: string; note?: string; children: ReactNode; id?: string }) {
   return <StorySection id={id} title={title} description={note}>{children}</StorySection>
 }
 export function Specimen({ label, size, line, weight }: { label: string; size: string; line: string; weight?: string }) {