Fix checkout payload so /checkout stops returning 500

[sentry]

This pull request was triggered by a Seer handoff from Sentry.

Fixes ANDROID-KV

Root cause

The checkout request built in MainFragment.buildJSONPostData() labelled each cart item with name, but the /products response and the backend /checkout handler both use title. When an item was out of stock the backend looked up item['title'], hit a KeyError, and returned HTTP 500. The payload was also missing cart.total, which the backend reads on the all-in-stock path, so that branch failed the same way. Since the app calls processDeliveryItem() on any non-2xx checkout response, and that method unconditionally throws BackendAPIException("Failed to init delivery workflow"), every failed checkout surfaced as this error.

Solution

Send title for each cart item (still sourced from the store item name) and include the computed cart.total, matching the payload the backend and the web client expect. With this shape the checkout succeeds — or returns a normal partial/failed status for genuinely out-of-stock items — instead of 500ing and triggering the delivery workflow error.

Verification

The Android toolchain isn't available in this environment, so the payload builder was replicated in a standalone harness and its output run through a simulation of the backend /checkout inventory logic. The old payload reproduced KeyError: 'title' → "Error validating enough inventory for product"; the new payload returns success, partial, and failed statuses correctly for full, partial, and empty inventory.

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
Android	com.example.vu.android	24.12.26 (241226)	release
Android	com.example.vu.android	24.12.26 (241226)	debug
Android	com.example.vu.android	24.12.26 (241226)	release

⚙️ android Build Distribution Settings

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (21c77a4) to head (92f450b).

Files with missing lines	Patch %	Lines
.../example/vu/android/empowerplant/MainFragment.java	0.00%	4 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #265   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
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  Files         16      16           
  Lines        883     886    +3     
  Branches      67      67           
=====================================
- Misses       883     886    +3     

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