fix: improve UX feedback, memoization consistency, and docs accuracy

[eren-karakus0]

Summary

Four targeted improvements to code quality and user experience:

• UX: Clipboard copy feedback — Added toast notifications when copying wallet or storage account addresses in the Header dropdown. The app already uses sonner for toasts, but the copy actions had no user feedback.
• React: Memoization consistency — Wrapped handleFileChange in useCallback in BlobUploader to match the pattern used by all other event handlers (handleUpload, handleFileInputClick).
• React: Key prop cleanup — Simplified the uploaded blob list key from `${blob.name}-${index}` to blob.name, since blob names are enforced unique by the duplicate check. Removes the array index anti-pattern.
• Docs: Node.js version — Fixed README prerequisite from "Node.js 18+" to "Node.js 22+" to match the engines field in package.json.

Changes

File	Change
src/components/Header.tsx	Add toast.success() on clipboard copy, import toast from sonner
src/components/BlobUploader.tsx	Wrap handleFileChange in useCallback, simplify key prop
README.md	Fix Node.js version requirement (18+ → 22+)

Test plan

• Biome lint passes on all changed files
• No behavioral changes beyond added toast feedback
• Existing test suite unaffected (changes are additive)

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Note

Low Risk
Changes are limited to UI feedback, React memoization/key hygiene, and documentation; no protocol/auth/data-flow logic is altered.

Overview
Improves small UX and React correctness details across the demo.

In Header, copy-to-clipboard actions for wallet and storage addresses are now async and show sonner success toasts after copying.

In BlobUploader, handleFileChange is wrapped in useCallback (matching other handlers) and the uploaded blob list key is simplified to blob.name now that duplicates are prevented. The README prerequisite is updated from Node 18+ to Node 22+.

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