fix(archive): honor PreserveSymlinks and reject duplicate entry names

[lovehunter9]

Summary

• When preserveSymlinks=false, dereference symlink sources before handing them to 7z (7z's -snl is a no-op for zip/tar in our build, so the flag alone couldn't honor "do not preserve").
• Pass -snl through the compound-tar (tar.gz/tar.bz2/tar.xz) path, which previously ignored PreserveSymlinks entirely.
• Reject sources that would collapse to the same archive entry name (e.g. a symlink dereferenced onto its target, or two same-named files) with a clear up-front error instead of a raw 7z "Duplicate filename" failure.

Test plan

• Compress file + symlink-to-file with preserve on → archive keeps the symlink as a link.
• Same sources with preserve off → clear error: both would be archived as the same name.
• tar.gz / 7z / zip all behave consistently.

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