feat: Add fiat payment confirmation flow with headless ramp integration placeholder

[OGPoyraz]

Description

Add fiat payment confirmation flow with headless ramp integration placeholder

Summary

• When a user confirms a transaction with fiat payment selected and no order yet, the confirm button now triggers the ramp purchase flow instead of submitting the transaction directly (startHeadlessBuy call is placeholder — will be uncommented once the Ramps team delivers the headless API)
• After ramp purchase completes and orderCode lands in state, useTransactionPayAutoFiatSubmission auto-submits the transaction so the FiatStrategy in TransactionPayController can poll the order and relay funds
• Auto-submission is deduplicated per orderCode and retries on failure
• getStrategy in controller init now routes transactions with a selected fiat payment method to FiatStrategy instead of the default Relay
• Non-fiat confirmation flow is completely unchanged
• Depends on feat: Implement FiatStrategy submit flow with order polling and relay execution core#8347 — @metamask/transaction-pay-controller dep bump required before merge

Changelog

CHANGELOG entry:

Related issues

Fixes:

Manual testing steps

Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]

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✅ E2E Fixture Validation — Schema is up to date
17 value mismatches detected (expected — fixture represents an existing user).
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