Fix: Correct delivery workflow initialization on checkout

[sentry]

This PR addresses the MainFragment$BackendAPIException: Failed to init delivery workflow error.

Root Cause:
The issue stemmed from two main problems in MainFragment.java:

1. The processDeliveryItem() method was being called even when the checkout API request to flask.empower-plant.com/checkout failed (returned HTTP 500 or an IOException).
2. The processDeliveryItem() method itself contained a hardcoded throw new BackendAPIException(...), meaning it would always throw an exception whenever it was invoked, regardless of the actual delivery workflow status.

Solution:

1. Removed processDeliveryItem() calls from checkout failure paths: The onResponse callback's !success branch and the onFailure callback no longer invoke processDeliveryItem(). Instead, they now correctly finish the Sentry transaction with SpanStatus.INTERNAL_ERROR.
2. Moved processDeliveryItem() to the success path: processDeliveryItem() is now only called within the onResponse callback when response.isSuccessful() is true, ensuring it's only triggered after a successful checkout.
3. Fixed processDeliveryItem() logic: The hardcoded throw new BackendAPIException(...) has been removed from processDeliveryItem(). The method now correctly logs and sets the span status to OK, simulating a successful delivery workflow initialization.

Fixes ANDROID-NQ

_{@sentry <feedback>: Autofix iterates on these changes
@sentry stop iterating: Autofix stops iterating on this run}

[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 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (21c77a4) to head (e2cae7a).

Files with missing lines	Patch %	Lines
.../example/vu/android/empowerplant/MainFragment.java	0.00%	6 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #274   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         16      16           
  Lines        883     879    -4     
  Branches      67      66    -1     
=====================================
+ Misses       883     879    -4     

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