docs: restructure README and add backend README

[Kanishkamangal09]

Summary

This PR restructures the project documentation by simplifying the root README and moving backend specific documentation into a new backend/README.md.

Changes

• Simplified the root README to serve as a project entry point.
• Added a new backend/README.md for backend specific documentation.
• Moved detailed feature documentation from the root README.
• Moved local development instructions to the backend README.
• Added dependency information for Vault Web, Deploy, and ClamAV.
• Added links between the root README and backend documentation.
• Removed duplicated documentation to keep instructions in a single place.

Closes #113

[Copilot]

Pull request overview

This PR restructures project documentation by slimming down the root README.md into a high-level entry point and moving backend-specific feature and setup documentation into a new backend/README.md, aligning with the goals in issue #113.

Changes:

• Simplified root README to focus on ecosystem orientation, quick start, and links to deeper docs.
• Added backend/README.md containing backend responsibilities, feature details, and local development guidance.
• Centralized detailed documentation to reduce duplication and keep instructions in one place.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
README.md	Reduced to an entry-point README with feature bullets, quick start, and dependency overview linking to backend docs
backend/README.md	New backend-focused README with responsibilities, feature/API details, and local dev + test instructions

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[DenizAltunkapan]

@Kanishkamangal09 thank you for your contribution