feat: add batch PDF to PNG conversion with ZIP download

[Ashvin-KS]

📄 Pull Request

🔗 Issue Reference

Closes #309

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📝 Summary

• Problem: Users could only convert one PDF to PNG at a time. Bulk workflows (many PDFs) required running the existing tool repeatedly, which was slow and tedious.
• Solution: Adds a new Batch PDF to PNG tool at /pdf-to-png-batch. Users select (or drag-and-drop) multiple PDF files, choose an image scale, and convert every page of every file to PNG. All results are packaged into a single ZIP download. Each PDF's pages are namespaced into their own sub-folder inside the ZIP.

Changes

• New file frontend/src/pages/PdfPngBatch.jsx — self-contained batch tool: multi-file selection, queued per-file conversion, per-file + overall progress bars, error handling, and ZIP assembly. Conversion reuses the same pdfjs-dist rendering pipeline as the existing PdfPng.jsx.
• frontend/src/App.jsx — lazy-loads PdfPngBatch and registers the /pdf-to-png-batch route inside the shared Layout.
• frontend/src/data/toolsData.jsx — registers the tool in the PDF Tools category (Layers icon, description, path, gradient).

No new dependencies are introduced — jszip, pdfjs-dist, framer-motion, sonner, lucide-react, clsx, and tailwind-merge are all already used elsewhere in the project.

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🖼️ Screenshots (if applicable)

Multi-file queue with remove buttons, a scale selector, a "Convert N PDFs" action, and dual progress bars (current file % and overall %), followed by a ZIP download.

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✅ Checklist

• My code follows the project's coding conventions
• I have tested all impacted features
• I have updated or added necessary documentation

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🔗 Related Issues / PRs

• feat: Add batch PDF conversion support for multiple files #309 — feat: Add batch PDF conversion support for multiple files

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🎓 Open Source Program Participation

Program Name: GSSoC 2026

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💬 Additional Notes

• Files are processed sequentially (as the issue's implementation notes request) to avoid memory spikes from rendering many PDFs concurrently.
• An overall progress bar is computed from the true total page count across all selected PDFs, so it accurately reflects remaining work.
• When only a single PDF is queued, its PNGs are placed at the ZIP root (no sub-folder) so the output is identical to a one-off conversion.
• The image scale selector (1x/2x/3x) lets users trade speed against output quality, matching the existing single-file tool's behaviour.

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[Durgeshwar-AI]

@Ashvin-KS please check the current pdf to png and work on it no new tool.