fix(download): keep downloading sources past a failed file

[bhdnb]

Summary

download sources fetched project files one at a time and aborted on the first error. Every file after the failing one went untried, and the files already written were never reported.

It now downloads four files at a time and keeps going when one fails, the same way upload sources and upload translations already work:

• every failure is printed
• --output json|toon|plain still lists the files that were written, sorted by path
• the command then exits 1 with Current execution finished with errors

Behaviour changes

	Before	After
Order	one file at a time	4 concurrent (runConcurrently, same limit as upload)
One file fails	abort, later files skipped	remaining files still downloaded
Exit code on failure	the failing request's own code (102, 103, …)	1, as upload does
Text output order	project path order	completion order

Difference from Java. DownloadSourcesAction also runs in parallel and keeps going, but CrowdinExecutorService.afterExecute only prints the error and the command exits 0. That part is deliberately not ported. A run that failed to write files should not exit 0, the same reasoning as #1106.

Changes

• DownloadCommand.sourcesAction: the sequential loop is replaced with runConcurrently + reportFailures, and machine-format output is sorted. The --reviewed path is unchanged, since it only extracts from a local archive.
• reportFailures / EXECUTION_FINISHED_WITH_ERRORS move from upload/uploadFailures.ts to common/failures.ts, now that download shares them. The two upload imports are updated.
• Fixed a stale comment in translationsAction that described the old sequential sources loop.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.22%. Comparing base (175b5cd) to head (159dfe3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1116      +/-   ##
==========================================
+ Coverage   92.21%   92.22%   +0.01%     
==========================================
  Files         142      142              
  Lines       11500    11506       +6     
==========================================
+ Hits        10604    10610       +6     
  Misses        896      896              

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