GT-2601: Download translation files from CDN with SHA-256 verification

[frett]

Summary

• Introduces ApiConfig to consolidate API/CDN base URL configuration, replacing the scattered @Named string injection
• Adds CdnApi (Retrofit) for downloading published translation files from the CDN, with base URLs configured per flavor (mobilecontent-stage.cru.org / mobilecontent.cru.org)
• Verifies SHA-256 checksum and byte size when storing downloaded files, rejecting any file that doesn't match the manifest metadata
• Prefers the CDN when downloading published translation files, falling back to the existing TranslationsApi on 4xx errors or IOException

Test plan

• New unit tests cover: CDN preferred over API, fallback to API on CDN 404, fallback on IOException, both sources failing returns false, correct/wrong SHA-256 accepted/rejected, correct/wrong size accepted/rejected
• Run ./gradlew :library:download-manager:test to verify all download manager tests pass
• Run ./gradlew :build-logic:ktlintCheck ktlintCheck to verify code style
• Smoke test on stage build: download a tool and confirm it completes successfully

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 65.90909% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.06%. Comparing base (912cd6a) to head (3af7a56).

Files with missing lines	Patch %	Lines
.../src/main/kotlin/org/cru/godtools/api/ApiModule.kt	0.00%	7 Missing ⚠️
...odtools/downloadmanager/GodToolsDownloadManager.kt	87.87%	1 Missing and 3 partials ⚠️
...ain/kotlin/org/cru/godtools/dagger/ConfigModule.kt	0.00%	3 Missing ⚠️
.../src/main/kotlin/org/cru/godtools/api/ApiConfig.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4424      +/-   ##
===========================================
+ Coverage    51.99%   52.06%   +0.07%     
===========================================
  Files          454      455       +1     
  Lines        12075    12105      +30     
  Branches      2092     2096       +4     
===========================================
+ Hits          6278     6303      +25     
- Misses        5181     5188       +7     
+ Partials       616      614       -2     

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