feat: test archive integrity without extracting

[nextestudios]

Summary

• New Test integrity action (North on an archive in the file list, or in the menu inside an open archive).
• IArchiveService.TestAsync / SafeExtractor.TestAsync: reads every file entry through the same path as extraction and discards the data (Stream.Null). The read/verify loop (limits on bytes actually read, declared size, CRC, AE-2 CRC-0 skip) was factored into CopyVerified, shared by extraction and test, so both enforce the same checks. Nothing is written: no dedicated folder, no staging.
• One ItemResult per entry: succeeded (CRC matched), succeeded with NoChecksum (TAR/GZ/AES AE-2: read fully, nothing to compare), failed (with the reason), not processed (after cancel or a fatal stream error).
• Runs in the operation queue (OperationKind.TestArchive) with progress and cancel; password-protected archives use the existing password keyboard (wrong password asks again). The result dialog lists counts, names failing entries and states it is not a virus scan.
• README/GUIDE (both languages), docs/archive-support.md and both changelogs updated. README no longer lists ZIP AES/ZIP64 as unvalidated (done in test: validate ZIP64 extraction with generated fixtures #131 and feat: validate WinZip AES ZIP extraction #137).

Tested in CI

• ArchiveTestTests: corrupted ZIP names the failing entry and the temp dir is unchanged; good ZIP reports OK; TAR entries flagged as no checksum; cancelling from a progress report stops and marks the rest not processed.
• Journey: Actions → Test integrity on a corrupted ZIP shows the failing entry, the "not a virus scan" note and extracts nothing.

Manual checks

• None beyond the usual visual review of the result dialog.

Closes #66

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