Billing cleanup and fuller parameter docs

Billing

• Web search is billed per call

• Removed a batch of price components that were configurable but never actually charged

• The pay-as-you-go table's columns follow the components that really bill

Docs

• Every parameter in the API reference now has a property description, nested ones included

• Model pages no longer restate prices — pricing lives in one place

• Supported aspect ratios widened to 14

Fixes

• Media usage could be dropped entirely, showing a zero bill; fixed

• Image tokens are no longer charged a second time at text rates