Billing UI: inconsistent 'Buy Credit' vs 'Add Credits' verbiage

Summary

The Anthropic billing page at console.anthropic.com uses the label "Buy Credit" on the button, but other Anthropic documentation and in-product references (including Claude Code error messages like "Your credit balance is too low... go to Plans & Billing to upgrade or purchase credits") refer to the same action as "Add Credits".

Impact

Minor but causes user confusion — users following instructions to "add credits" don't immediately recognize that "Buy Credit" is the same action.

Suggested Fix

Standardize on one label across the console UI and all documentation/error messages. Either:

• Change the button to "Add Credits", or
• Update all references in docs/error messages to say "Buy Credit"

Low effort, high clarity win.