Goal
Gate the entire fiat payment feature behind the confirmations_pay_fiat LaunchDarkly flag so it can be enabled incrementally via remote config.

Scope

• Read the confirmations_pay_fiat remote feature flag (already created in LaunchDarkly) via selectRemoteFeatureFlags.
• Add a selectPayFiatEnabled selector following the existing pattern (selectMetaMaskPayFlags, selectGasFeeTokenFlags, etc.):
  • Read featureFlags?.confirmations_pay_fiat from remote flags.
  • Extract an enabled boolean, defaulting to false.
• Expose a convenience hook (e.g. useIsPayFiatEnabled) or just use the selector directly — follow whichever pattern the codebase prefers.
• All downstream fiat-related UI/logic will early-return when the flag is off.

Acceptance criteria

• selectPayFiatEnabled reads confirmations_pay_fiat from remote feature flags.
• Returns false when the flag is absent or enabled is not true.
• Returns true when LD has confirmations_pay_fiat.enabled = true.
• No UI or behavioral changes when the flag is off.
• Unit tests covering: flag absent, flag false, flag true.

Out of scope

• Any fiat payment UI or logic — just the flag selector.

Key files

• app/selectors/featureFlagController/confirmations/index.ts
• app/selectors/featureFlagController/confirmations/index.test.ts