Update subscription flow welcome page

[cmonfortep]

Task/Issue URL: https://app.asana.com/1/137249556945/project/72649045549333/task/1210461583262419?focus=true

Description

Updates JS messaging in subscription flows welcome pages.

Touched methods:

• Adds getAuthAccessToken
• Adds getFeatureConfig
• Adds Duck.ai support in featureSelected

Feature flagging:

• privacyProFeature.subscriptionMessaging() -> enables getFeatureConfig
• privacyProFeature.duckAiPlus() -> signales FE Duck.ai is enabled
• Token is not affected by FF

Steps to test this PR

Feature 1

• apply patch attached in the Asana task (that will target staging and specific FE sandbox)
• install the branch
• Ensure you don't have a subscription
• Start purchase a subscription
• In the landing page, scroll to the bottom.
• Ensure Duck.ai appears in the comparison chart.
• Purchase a subscription
• After purchase, welcome page should list Duck.ai as a card
• Click on the Card
• Ensure pixel m_privacy-pro_welcome_paid-ai-chat_click emits
• Ensure you navigate to Duck chat (this branch doesn't have the code to signal the token so you won't see the subscriber mode)

Feature 2

• Go to feature flags and disable privacypro - duckAiPlus
• Cancel and delete your subscription
• Repeat the process again
• Ensure in Landing page comparison chart, Duck.ai doesn't show.
• Ensure when subscription is purchased, there's no Duck.ai card

Feature 3

• Remove all files changed in previous patch
• Apply standard patch from https://app.asana.com/1/137249556945/project/1209991789468715/task/1210448620621729?focus=true (no FE sandbox)
• install the branch
• Ensure you don't have a subscription
• Purchase a subscription
• ensure purchase succeeds
• ensure no duck.ai is present

UI changes

Before	After
!(Upload before screenshot)	(Upload after screenshot)

[cmonfortep]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Update subscription flow welcome page #6260 👈 (View in Graphite)
• Include Duck ai in subscription settings #6200 : 6 other dependent PRs (#6217 , #6350 , #6363 and 3 others)
• develop

This stack of pull requests is managed by Graphite. Learn more about stacking.

[Copilot]

Pull Request Overview

Adds support for capturing and acting on a new “Duck AI” feature selection during the subscription welcome flow, including pixel reporting, ViewModel/Activity handling, and JS messaging extensions.

• Introduces a DUCK_AI constant and corresponding pixel event for onboarding clicks.
• Extends SubscriptionWebViewViewModel and SubscriptionsWebViewActivity to emit and handle a new GoToDuckAI command using DuckChat.
• Adds two new JS message handlers (getAuthAccessToken and getFeatureConfig) and feature toggles (duckAiPlus, subscriptionMessagingV2).

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
subscriptions-impl/src/test/java/com/duckduckgo/subscriptions/impl/ui/SubscriptionWebViewViewModelTest.kt	Tests for GoToDuckAI command emission and pixel reporting
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/ui/SubscriptionsWebViewActivity.kt	Injects DuckChat, handles GoToDuckAI by calling openDuckChat()
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/ui/SubscriptionWebViewViewModel.kt	Maps DUCK_AI to GoToDuckAI and dispatches onboarding Duck AI pixel
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/pixels/SubscriptionPixelSender.kt	Adds reportOnboardingDuckAiClick() to interface and implementation
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/pixels/SubscriptionPixel.kt	Defines ONBOARDING_DUCK_AI_CLICK pixel entry
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/messaging/SubscriptionMessagingInterface.kt	Adds GetAuthAccessTokenMessage & GetFeatureConfigMessage handlers and imports PrivacyProFeature
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/SubscriptionsConstants.kt	Defines DUCK_AI constant
subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/RealSubscriptions.kt	Introduces duckAiPlus() and subscriptionMessagingV2() toggles
subscriptions-impl/build.gradle	Adds dependency on :duckchat-api

Comments suppressed due to low confidence (1)

subscriptions/subscriptions-impl/src/main/java/com/duckduckgo/subscriptions/impl/messaging/SubscriptionMessagingInterface.kt:319

• No unit tests cover the new GetAuthAccessTokenMessage and GetFeatureConfigMessage handlers. Consider adding tests to verify both the success and failure JSON responses for these methods.

    private inner class GetAuthAccessTokenMessage(