Links IAP Leo purchase to desktop

[SergeyZhukovsky]

Resolves brave/brave-browser#35983

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[kjozwiak]

Verification PASSED on Pixel 8 Pro running Android 14 using the following build(s):

Brave | 1.65.2 Chromium: 122.0.6261.43 (Official Build) canary (64-bit)
Revision | 241c70d7f059bd6e2026f12c9928f56f3608e148
OS | Android 14; Build/UQ1A.240205.004; 34; REL

• launched 1.65.2 Chromium: 122.0.6261.43 and enabled Leo staging
  • Hamburger Menu -> Settings -> Developer options -> QA Preferences
• once enabled, purchased Leo premium via Hamburger Menu -> Settings -> Leo -> Go Premium
• once Leo has been purchased, tapped on Link purchase to your Brave account via the Leo settings
• ensured that https://account.bravesoftware.com was being used (Staging)
• used an account that doesn't have any Premium products
• once logged into the Brave Account, tapped on Link my subscription now
  • ensured that the Success! Your subscription is now linked message was displayed once linked
• ensured that Leo appeared as a purchased premium product
  • ensured that Purchased on Android is visible/being displayed

Example	Example	Example	Example	Example

Example	Example	Example	Example

Once the above was completed/verified, launched 1.62.165 Chromium: 121.0.6167.184 on Win 11 x64 using the following:

• brave.exe --enable-logging=stderr --env-leo=staging --env-ai-chat.bsg=dev --env-ai-chat-premium.bsg=dev

Once launched, went through the following using 1.62.165 Chromium: 121.0.6167.184 on Win 11 x64

• logged into the same account that was used above via https://account.bravesoftware.com/account/
• once logged in, verified that Leo was a product that appeared as Purchased
  • ensured that Purchased on Android is visible/being displayed
• clicked on Refresh Leo and ensured that new credentials were pulled and Leo switched to Premium on the desktop
• ensured that Premium appeared throughout the UI and that Unlimited appeared next to each LLM (indicating Premium)

Example	Example	Example	Example	Example