Feature/standalone file uploader

[ErykKul]

What this PR does / why we need it:

This PR adds a standalone file uploader (DVWebloader V2) that can be built as an independent bundle and embedded in external pages. It reuses the existing FileUploaderPanelCore component to avoid code duplication.

Key features:

• Standalone bundle: Single JS file (~1.5MB) that can be loaded independently from the main SPA
• Shared components: Reuses FileUploaderPanelCore for the accordion uploader UI
• API key authentication: Uses URL parameters for configuration (siteUrl, datasetPid, key)
• S3 configuration: Supports window.dvWebloaderConfig for S3 tagging, retries, and timeout settings
• Configurable S3 tagging: Can disable S3 tagging for storage backends that don't support it

Which issue(s) this PR closes:

• Related to DVWebloader modernization effort (https://github.com/gdcc/dvwebloader)

Special notes for your reviewer:

• The standalone uploader is built with npm run build-uploader using vite.config.uploader.ts
• It requires @iqss/dataverse-client-javascript to export FilesConfig (see feat: add configurable file upload options and related tests dataverse-client-javascript#403)
• The bundle entry point is src/standalone-uploader/index.tsx
• StandaloneFileUploaderPanel.tsx is a thin wrapper (~70 lines) around FileUploaderPanelCore

Suggestions on how to test this:

1. Build the standalone bundle: npm run build-uploader
2. Serve the dist-uploader folder
3. Open dvwebloaderV2.html?siteUrl=http://localhost:8080&datasetPid=doi:10.5072/FK2/XXXXX&key=YOUR_API_KEY
4. Test file upload via drag-drop and file picker
5. Verify files are added to the dataset

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Yes - adds a new standalone page for file uploads. The UI reuses the existing file uploader accordion from the SPA.

Is there a release notes or changelog update needed for this change?:

Yes - new feature: Standalone file uploader bundle for embedding in external pages (DVWebloader V2)

Additional documentation:

Configuration via window.dvWebloaderConfig (set in HTML before bundle loads):

window.dvWebloaderConfig = {
    useS3Tagging: true,      // Disable for S3 backends without tagging support
    maxRetries: 3,
    uploadTimeoutMs: 0,
    disableMD5Checksum: false
};

URL parameters:

• siteUrl - Dataverse instance URL (required)
• datasetPid - Dataset persistent ID (required)
• key - API key (required)
• dvLocale - Language code (optional, default: en)

[coveralls]

coverage: 98.063% (+0.3%) from 97.795%
when pulling 97722e1 on feature/standalone-file-uploader
into 48dd9ff on develop.