Admin pricing overrides can now apply to managed policies

What

• The gateway config validator, which previously required an admin: block for pricing settings to take effect, now also accepts a managed: block containing at least one policy, since both the admin spend meter and the modelPricing sent to clients read the same pricing config.
• The gateway can now compute a per-deployment modelPricing object (a price multiplier plus per-model overrides) from an admin.pricing-style config, and merges it into each managed policy's cli settings, but only for policies that don't already specify their own modelPricing. It logs how many policies received the pushed pricing.
• The dead-code checker that warns about pricing overrides that can never take effect was updated for the case where there's no admin/meter block: in that case, an override is only considered reachable if it sits on the first upstream that would actually serve that model.

Why This lets pricing overrides configured under admin.pricing reach managed-policy clients automatically, and improves the accuracy of warnings about pricing overrides that would silently never apply.