A controversial proposal to impose a one-time tax on California’s billionaires has officially qualified for the November ballot, setting up a high-stakes political battle in the state. The measure, backed by a labor union coalition, would target residents with wealth above $1bn and channel the revenue into public services including healthcare, education and food assistance. The proposal has sharply divided Silicon Valley and state leaders, with tech figures including Mark Zuckerberg, Sergey Brin