Fix: fixed dead links

[letmehateu]

Fixed dead links in ens-names.md, contracts.md and overview.md

Description

• Now the images load everywhere where it should
• The non-existent link to the FName API reference has been fixed.

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PR-Codex overview

This PR updates the paths for image assets and modifies a link in the documentation to ensure correct referencing in the docs directory.

Detailed summary

• Updated image paths in docs/learn/architecture/contracts.md, docs/learn/architecture/overview.md, and docs/learn/architecture/ens-names.md to use relative paths.
• Modified the link to the FName API reference in docs/learn/architecture/ens-names.md for correct referencing.

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