fix(settings): VPN polish - CMS copy on set-password, repeat PW when Sync isn't decoupled, service_welcome routing

[LZoog]

Because:

• The CMS text for passwordless OTP users when Sync is not decoupled is not rendered on the set password page
• The repeat password field is not displayed when Sync is not decoupled
• Mobile users should not be navigated to the service welcome screen for VPN because the browser automatically closes it

This commit:

• Renders the CMS text and repeat password fields accordingly
• Adds a Mobile check and does not navigate those users to the service welcome screen
• Returns a fixed requiresPasswordForLogin value from signup mock instead of rederiving it

closes FXA-14047
closes FXA-14088

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

[Copilot]

Pull request overview

This PR polishes password-setting and post-verification behavior for VPN / non-decoupled Sync scenarios by ensuring the correct CMS copy and password confirmation UI are shown, and by adjusting VPN-specific routing after signup confirmation.

Changes:

• Prefer CMS description copy on the PostVerify Set Password page for all arrival paths, with hardcoded text as fallback.
• Update Signup password-confirmation logic to depend on whether a password is required for key derivation (requiresPasswordForLogin), not only on Sync.
• Avoid navigating mobile VPN users to /post_verify/service_welcome to prevent a brief “blip” before the client closes the webview; add tests/stories/mocks updates.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/fxa-settings/src/pages/Signup/mocks.tsx	Extends signup mocks to include requiresPasswordForLogin and adjusts OAuth-native mock signature.
packages/fxa-settings/src/pages/Signup/interfaces.ts	Extends signup integration types to include requiresPasswordForLogin.
packages/fxa-settings/src/pages/Signup/index.tsx	Uses requiresPasswordForLogin(supportsKeysOptionalLogin) to decide whether to show repeat-password confirmation.
packages/fxa-settings/src/pages/Signup/index.test.tsx	Updates expectations and adds coverage for keys-optional vs non-optional password confirmation behavior.
packages/fxa-settings/src/pages/Signup/container.test.tsx	Updates the integration mock to include requiresPasswordForLogin.
packages/fxa-settings/src/pages/Signup/ConfirmSignupCode/index.tsx	Skips service_welcome navigation for mobile VPN to avoid UI “blip”.
packages/fxa-settings/src/pages/Signup/ConfirmSignupCode/index.test.tsx	Adds test to ensure no navigation occurs for mobile VPN.
packages/fxa-settings/src/pages/PostVerify/SetPassword/index.tsx	Renders CMS description regardless of arrival reason; falls back to reason-specific hardcoded copy.
packages/fxa-settings/src/pages/PostVerify/SetPassword/index.test.tsx	Adds assertions for CMS-vs-fallback copy across OTP/passkey paths; refactors CMS test data usage.
packages/fxa-settings/src/pages/PostVerify/SetPassword/index.stories.tsx	Adds OTP-with-CMS story variant.
packages/fxa-settings/src/pages/mocks.tsx	Adds PostVerifySetPasswordPage to shared MOCK_CMS_INFO.

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[LZoog]

I had something like this originally, and then I opted to simplify it. I'd rather leave it as-is where you just pass in requiresPasswordForLogin depending on what you're testing.