Description

This PR fixes pure-black dark mode feedback for clipboard and network-change alerts (TMCU-801) by removing the legacy GlobalAlert stack and migrating call sites to the design-system toast() API.

Why: GlobalAlert relied on scrim/overlay tokens that collapse visually in pure-black dark mode, making success and warning banners hard to read.

What changed:

• Remove GlobalAlert, the alert Redux action/reducer, and related persist/test wiring
• Add a single root <Toaster /> in Root inside a full-screen overlay so toasts render above navigation
• Migrate former GlobalAlert call sites to toast():
  • Network switch warning (switchNetwork.ts)
  • NFT address copied success (NftDetails.tsx)
  • Legacy clipboard path in AccountOverview (dead code, updated for consistency)
• Remove redundant per-screen <Toaster /> instances from Multichain Accounts screens
• Revert unrelated SimpleNotification story/test changes; storybook.requires.js matches main

Changelog

CHANGELOG entry: null

Related issues

Fixes: TMCU-801

Manual testing steps

Feature: MMDS toast replaces GlobalAlert in pure-black dark mode

  Scenario: Success toast after copying an NFT address
    Given MM_PURE_BLACK_PREVIEW="true" in .js.env
    And the app is rebuilt with yarn watch:clean
    And the app theme is set to Dark
    When the user copies an NFT contract address from NFT Details
    Then a success toast appears above the bottom navigation
    And the message reads "Token address copied to clipboard"

  Scenario: Warning toast after switching networks
    Given MM_PURE_BLACK_PREVIEW="true" in .js.env
    And the app theme is set to Dark
    When the active network changes (e.g. via deeplink or network switch)
    Then a warning toast appears above the bottom navigation
    And the message includes "Network changed to"

  Scenario: Light mode appearance is unchanged
    Given MM_PURE_BLACK_PREVIEW is off or the app is in light mode
    When success or warning toasts are triggered
    Then the toast is legible and dismissible

Screenshots/Recordings

After screenshots (pure black dark mode, 350px width) are on the Files changed tab as inline file comments:

• Success toast — app/components/Views/NftDetails/NftDetails.tsx
• Warning toast — app/util/networks/switchNetwork.ts

Images: https://github.com/MetaMask/metamask-mobile/tree/screenshots/visual-regression/pr-32914/after

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Performance checks (if applicable)

• I've tested on Android
  • Ideally on a mid-range device; emulator is acceptable
• I've tested with a power user scenario
  • Use these power-user SRPs to import wallets with many accounts and tokens
• I've instrumented key operations with Sentry traces for production performance metrics
  • See trace() for usage and addToken for an example

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.