Replaces the demolition scaffold with the structural grid that Tasks 8-21
fill in. Root is a 4-row grid (topstrip / alertbanner / main / bottomticker)
with named grid-areas; the main row contains a 3-col sub-grid (left aside /
center section / right aside) at fixed 320px / 1fr / 320px. 100dvh, no body
scroll, ethos custom properties only — no template SCSS variables touched.
Adds --col-panel-width: 320px to the ethos token block (no magic number in
the layout module). index.tsx becomes a one-line re-export of Dashboard so
the lazy-route contract in routers.tsx stays unchanged.
No placeholder components. The empty <aside>/<section> elements are the
column containers themselves; subsequent tasks add real children inside
them rather than swap stub components.
Verified in browser at 1920x1080: rgb(10,10,10) bg, 320/1247/320 col rects,
1px var(--fg-4) rules between columns, body has no scroll. All 5 Plan 5
Task 7 Design QA boxes checked.
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