feat: Add “View Sample” fallback for multi-send CSV on /droppage (Web…

[col3name]

Pull Request: Add “View Sample” fallback for multi-send CSV on /droppage (WebView fix)

Summary

This PR adds a “View Sample” fallback button to /droppage so users inside the MyTonWallet in-app WebView (Android/iOS) can access the multi-send sample CSV.
Downloading via Blob + a.click() is blocked in WebViews, so the sample file could not be downloaded previously.

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What’s changed

• Added “View Sample” button on /droppage
• Opens a modal (or inline view) showing the full multi-send sample CSV
• Allows users to copy the CSV manually
• Normal download behavior kept for browsers where it works
• Improves UX for users accessing multisend through the MyTonWallet old design → Multi Send flow

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Why

Users opening multisend from inside the MyTonWallet app (old design → long press Send → Multi Send) were unable to download the required sample CSV because:

• WebViews block blob: URLs
• WebViews block programmatic downloads (a.click())

This PR ensures they can still access the CSV content.

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Related Issue

Fixes: #307

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