feat: build client-side tabular Data Export capabilities (CSV / JSON format) for user records

[prakshithamalla-art]

Description

Closes #1487

This PR builds localized client-side data archive export utilities directly inside the authenticated dashboard user settings view to satisfy DevTrack's zero vendor lock-in commitments.

Changes Made

• Created a completely isolated, standalone component DataExportCard.tsx under the components layout folder.
• Configured real-time batch async endpoint fetching that aggregates both core user preferences and active milestone metrics structures simultaneously.
• Formatted structured raw memory serialization strings mapping JSON formatting buffers alongside flattened row-by-row delimited CSV lines.
• Triggered anchor-link transient browser download blobs (application/json & text/csv) entirely on the client, avoiding any unnecessary server database overhead.

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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[Priyanshu-byte-coder]

This PR now has merge conflicts with main. Please rebase your branch against the latest main and force-push to resolve. Run: git fetch upstream && git rebase upstream/main

[Priyanshu-byte-coder]

This PR has merge conflicts with the current main branch. Please rebase your branch onto main, resolve the conflicts, and force-push. Once conflicts are resolved and the PR is marked as mergeable it will be reviewed for merging.

[Priyanshu-byte-coder]

This PR has developed merge conflicts after recent merges to main. Please rebase onto the latest main branch, resolve all conflicts, and force-push. Once the PR is conflict-free it will be reviewed for merging.