GET /api/quota/pools/[id]/usage returns { usage: snapshot }, but usePoolUsage
stored the whole wrapper, leaving usage.dimensions undefined. StackedAllocationBar
then dereferenced usage.dimensions[dimensionIndex] (undefined[0]) and crashed the
entire quota-share page for any pool that has allocations. Unwrap data.usage in the
hook + defensively guard usage.dimensions?.[i] / dim.perKey ?? [] in the bar.
