Fix non-printable keys in browser renderer

[to-be-coder]

Summary

• Fixes the sequence field in key event handling to only pass single-character keys, filtering out non-printable keys (e.g., Shift, Control, Alt) by checking event.key.length === 1

Test plan

• Verify that typing regular characters works as expected
• Verify that pressing non-printable keys (Shift, Control, Alt, etc.) no longer produces unintended input

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