[PM-33509] feat: Add BillingRepository and Hilt billing modules

[SaintPatrck]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-33509

📔 Objective

Create BillingRepository and BillingRepositoryImpl to abstract billing service operations into a repository layer, plus Hilt DI modules (BillingModule, BillingNetworkModule) for dependency injection wiring.

• BillingRepository interface exposes getCheckoutSessionUrl() and getPortalUrl() returning domain-specific sealed class result types (CheckoutSessionResult, CustomerPortalResult)
• BillingRepositoryImpl delegates to BillingService and maps response models using .fold() into the appropriate result types
• BillingNetworkModule provides BillingService via BitwardenServiceClient
• BillingModule provides BillingRepository as a singleton
• Unit tests cover success and failure paths for both repository methods

[github-actions]

Checkmarx One – Scan Summary & Details – 4c6ad90d-cd02-4290-9876-2bcafc1c3f0f

Great job! No new security vulnerabilities introduced in this pull request

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.67%. Comparing base (6d04c04) to head (d692519).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6674      +/-   ##
==========================================
- Coverage   85.80%   85.67%   -0.14%     
==========================================
  Files         807      851      +44     
  Lines       57331    58988    +1657     
  Branches     8362     8403      +41     
==========================================
+ Hits        49193    50536    +1343     
- Misses       5220     5520     +300     
- Partials     2918     2932      +14     

Flag	Coverage Δ
app-data	17.34% <100.00%> (-0.33%)	⬇️
app-ui-auth-tools	20.79% <0.00%> (-0.02%)	⬇️
app-ui-platform	15.67% <0.00%> (+0.60%)	⬆️
app-ui-vault	26.48% <0.00%> (+0.65%)	⬆️
authenticator	6.59% <0.00%> (-0.01%)	⬇️
lib-core-network-bridge	4.29% <0.00%> (+<0.01%)	⬆️
lib-data-ui	0.95% <0.00%> (-0.01%)	⬇️

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[claude]

Claude finished @SaintPatrck's task in 1m 57s —— View job

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Code Review: PR #6674

• Gather context and read all changed files
• Perform code review
• Post review findings

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Overall Assessment: APPROVE ✅

This PR introduces a new BillingRepository with Hilt DI wiring and custom result types (CheckoutSessionResult, CustomerPortalResult) for Stripe billing operations. The billing code follows established repository and result-type patterns, uses userFriendlyMessage for error display, and includes tests covering both success and failure paths. All prior review feedback has been addressed in subsequent commits.

Code Review Details

No findings.

[SaintPatrck]

Thanks @david-livefront