Use a single Consumption report card

Remove the separate World consumption introduction card and rename the report heading from Remaining content to Consumption. The report heading is now the page's h1; remove the unused introduction styles and align the existing route tests with the new accessible heading.

Related to #22 (closed) and #26 (closed); follows !77 (merged).

Validation: all 21 frontend tests pass and the production build succeeds (existing warnings remain). Rendered the built page using isolated synthetic report data on desktop and at 390px mobile width: exactly one main card, one Consumption heading, no page overflow. Report and gameplay behavior are unchanged.