style(storybook): unify content hierarchy and section spacing

- Story page frame: H2 16/24/700 -> 12px -> divider -> 16px -> content, sections 28px apart;
  StorySectionGrid keeps its 24px column gap
- Content indent (--sb-page-indent 16px, 12px at 640px and below): .sb-page-indent for information
  blocks; group boards (StateBoard / CardBoard, data-sb-board) indented once per section block so
  per-column boards keep their 24px gap
- Input / Select / Toggle Sizes grids take the same indent; field Labels unchanged
- Full-width Pattern previews (GNB, LNB, Loading Screen, Page Header) opt out with indent={false}
- Foundation/폰트: Text Colors name / usage / HEX levels, Font Family and Font Weight token lines,
  Specimens row spacing and indent; specimen values unchanged
- Guideline and WORKING_CONTEXT updated

src/patterns/loading-screen.stories.tsx

@@ -37,6 +37,7 @@ export const All: Story = {
       <StorySection title="Variants">
         {/* Default spans the full width; the other two share an equal 2-column row (1 column below 2 × 560px). */}
         <StateBoard
+          indent={false}
           min={560}
           states={[
             { id: "default", label: "Default", wide: true, children: <LoadingScreen /> },