Backend: GET /api/usage (requireJwtAuth) aggregates this user's prompt+
completion Transaction spend over today/7d/30d plus a per-model breakdown,
enriched with the org tier from CommerceClient. Response mirrors the
@hanzo/usage UsageSnapshot shape (providerId 'hanzo', totals, providerCost)
for one wire format across Hanzo products.
Frontend: new Usage settings tab beside Balance, reusing the UsageBar idiom;
useGetUserUsage hook follows useGetUserBalance; en localization strings added.
