fix: handle invalid shared chat data

[xeseing]

Summary

Handles invalid shared chat data safely when reading the share query parameter.

Changes

• Added a helper to parse shared chat messages safely
• Wrapped shared chat decompression and JSON parsing in a try/catch
• Falls back to an empty conversation when shared data is invalid
• Validates that parsed shared data is an array before passing it to useChat

Why

A malformed or invalid share query parameter can cause JSON.parse to throw and crash the chatbot. Shared links should fail gracefully instead of breaking the page.

Testing

• Reviewed src/components/chat.tsx
• Verified invalid shared chat data falls back to an empty message list
• Verified valid shared chat data still passes through when parsed as an array

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