Enable conflict detection in sneakernet transfers

[MrKeiKun]

Description
Sneakernet conflict detection was failing because ContentHash was never populated in FileManifest structures. This caused all conflict comparisons to return false, preventing detection of files with the same path but different content.

Referenced Issue: #46

[S4tvara]

Hi @MrKeiKun,
I was able to replicate the responses.

Please update the conflicts, and I'll merge the PR.

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[MrKeiKun]

@SubstantialCattle5

rabased and updated.

[S4tvara]

Cool, I'll review it later

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you're getting this error because your pr doesn't follow the new template, disregard it for now.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cmd/add.go	0.00%	24 Missing ⚠️

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