MetaMask#29906)

## **Description**

Adds a disabled/loading state to all interactive components on the MMPay
fiat confirmation screen while `startHeadlessBuy` is in progress. This
prevents user interaction during order preparation and provides clear
visual feedback via muted styling and a native loading spinner on the
CTA button.

Note that `isHeadlessBuyInProgress` is not currently used but it will be
integrated on MetaMask#28152

### Changes

- **`ConfirmationContext`**: Added `isHeadlessBuyInProgress` boolean +
setter to shared context so all target components can read the state
directly.
- **`ConfirmButton`**: Uses the design system `Button`'s built-in
`isLoading` / `loadingText` props to show a spinner with "Preparing
order" text.
- **`CustomAmount`**: Disables the amount input keyboard when loading.
- **`PayWithRow`**: Disables the token picker row; applies
`TextColor.Muted` / `IconColor.Muted` for consistent dimming while
preserving layout (arrow-down icon stays visible).
- **`BridgeFeeRow`**: Disables the tooltip ⓘ button and applies muted
text/icon colors.
- **`TotalRow`**: Applies muted text colors to label and value.
- **`Tooltip`**: Added `disabled` prop that guards `handlePress` and
passes `disabled` to the underlying `ButtonIcon` for true
non-interactivity.
- **`InfoRow` / `AlertRow`**: Added `tooltipDisabled` prop forwarded to
`Tooltip`; fixed `AlertRow` to only override label `variant` when an
alert is active (respects caller's prop otherwise).
- **Locale**: Added `confirm.preparing_order` string.

## **Changelog**

CHANGELOG entry: null

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: MMPay fiat loading state

  Scenario: Confirmation screen components are disabled during headless buy
    Given I am on the MMPay confirmation screen with a fiat payment method selected
    When I tap the confirm/add funds button to trigger startHeadlessBuy
    Then the CTA button shows a loading spinner with "Preparing order" text
    And the amount input keyboard is non-interactive
    And the "Pay with" row is dimmed and non-tappable
    And the "Transaction fee" row tooltip icon is dimmed and non-tappable
    And the "Total" row text is dimmed
    And no layout shifts occur on any row
```

## **Screenshots/Recordings**

### **Before**

### **After**



https://github.com/user-attachments/assets/7a227e71-562b-45a2-9ebd-76c3da45bf6c



## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [ ] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

#### Performance checks (if applicable)

- [ ] I've tested on Android
- [ ] I've tested with a power user scenario
- [ ] I've instrumented key operations with Sentry traces for production
performance metrics

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Touches confirmation-screen interaction/CTA enablement by introducing
a new shared loading flag that disables inputs and shows a loading
state; risk is mainly UX/flow regressions if the flag is set/cleared
incorrectly.
> 
> **Overview**
> Adds a new `isHeadlessBuyInProgress` flag (and setter) to
`ConfirmationContext` and threads it through MM Pay fiat confirmation
components to **freeze user interaction during order preparation**.
> 
> While this flag is true, the confirm CTA is disabled and shows a
native loading spinner with new copy (`confirm.preparing_order`), and
interactive rows/inputs (custom amount, pay-with picker, transaction-fee
tooltip) are disabled with muted styling. Also fixes `AlertRow` to only
override the `variant` color when an alert is present, and extends
`Tooltip`/`InfoRow` with a `disabled`/`tooltipDisabled` path to prevent
opening tooltips.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
cd87e35. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->