web: Dashboard sidebar and background should match the other pages #973

Found after deploying v0.1.3. Owner decision: the Dashboard's colours should match the rest of the pages.

Cause

The #906 redesign (PR #912) gave the Dashboard its own look on purpose, gated on the route:

• web/src/components/AppLayout.tsx:94-95: when location.pathname === "/", the sidebar Drawer paper uses bgcolor: "var(--brand)" and color: "var(--on-brand)".
• web/src/components/AppLayout.tsx:152: when pathname === "/", the main content box uses #faf7f2 (light) or #211b1e (dark).

Fix

Remove both Dashboard-only branches so the sidebar and content use the same theme surfaces as every other page, in light and dark. Check that nothing inside the Dashboard relied on the brand rail or warm canvas for contrast, and remove any styles that exist only for them.

Done when

The Dashboard's sidebar and content background match the other pages in light and dark mode, at desktop and phone widths.