AI Credits onboarding: Signer Key generation and import flow

[Copilot]

Adds the Setup-tab Signer Key onboarding flow, replacing user-facing Buyer Key terminology while preserving the existing wallet-derived generation mechanics. Import now validates AntSeed private keys and checks the configured operator before allowing progression.

• Signer Key UX
  • Added recommended Generate and Import choices.
  • Displays generated public/private keys with copy controls.
  • Added AntSeed setup guidance and backup warnings.
• Import and operator handling
  • Supports importing existing AntSeed signer keys.
  • Exposes current operator state to the UI.
  • Handles no operator, GoodDollar operator, and incompatible operator cases.
  • Blocks incompatible signers and returns users to selection.
• Coverage and copy
  • Updated onboarding, FAQ, stepper, and deep-link terminology.
  • Added Storybook fixtures and interaction coverage for generated and incompatible states.

const hasDifferentOperator =
  currentOperator !== ZERO_OPERATOR &&
  currentOperator !== configuredGoodDollarOperator

if (hasDifferentOperator) {
  // Require a different signer key before continuing.
}

• Fixes [PLAN] AI Credits onboarding: Signer Key generation and import flow #185

[Copilot]

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