(Feature) Add drag-and-drop arrangement for multi-file conversion tools

[AB527]

Description

This change adds a drag-and-drop file reordering interface to all multi-file conversion tools, allowing users to rearrange uploaded files before generating the final PDF.

The feature has been implemented across the following converters:

Image to PDF

• JPG to PDF
• PNG to PDF
• BMP to PDF
• TIFF to PDF
• WebP to PDF
• HEIC to PDF
• Image to PDF (generic)
• SVG to PDF

Document / Office to PDF

• CSV to PDF
• Word to PDF
• Excel to PDF
• PowerPoint to PDF
• ODT to PDF
• ODS to PDF
• VSD to PDF
• WPS to PDF
• Pages to PDF
• PUB to PDF

Previously, the output PDF page order depended on the upload sequence or file naming, which was inconvenient and error-prone when converting multiple files.

This update enables users to visually arrange files in the desired order before conversion, ensuring predictable and correct PDF structure.

The implementation reuses the same UI/UX pattern already used in the Merge PDFs workflow and the earlier JPG → PDF rearrangement feature, providing a consistent experience across the platform.

No external dependencies were introduced.

Fixes #353

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

🧪 How Has This Been Tested?

Please describe how you tested your changes so that maintainers can verify them. Include enough detail for someone else to reproduce your tests.

Checklist:

• Verified output manually
• Tested with relevant sample documents or data
• Wrote Vite Test Case (if applicable)

Expected Results:

• Drag-and-drop correctly updates file order
• Generated PDF pages follow the arranged sequence
• Consistent UI behavior across all multi-file tools
• No regressions in existing single-file or merge workflows

Actual Results:

• Files could be smoothly reordered using drag-and-drop
• PDFs were generated successfully with pages in the correct order
• The same rearrangement UI worked across all listed converters
• No UI glitches, runtime errors, or console warnings observed

Checklist:

• I have signed the Contributor License Agreement (CLA) or my organization has signed the Corporate CLA
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules