h-10 → h-15 (60px) in both the chat header and the /chat/new draft
header. 60px is an alignment, not just a size: it equals the sidebar's
LH wordmark band, so the header's border-b continues that band's bottom
edge as one horizontal line across the app — the sidebar's 'New session'
row begins exactly where the chat column's chrome ends.
Live: header border-b at y=60, wordmark band bottom at y=60. Gates:
typecheck, lint, 469/469.