Support input stream preview on keymap page

[cormoran]

Summary

• Add zmk-feature-input-stream proto bindings and a keymap input stream hook.
• Show a Stream mode toggle beside Reset All when zmk__input_stream is detected.
• Highlight streamed key positions in the keymap preview and play per-position beep tones.
• Add demo transport support for stream notifications.

Verification

• npm test -- --runTestsByPath src/hooks/__tests__/useInputStream.test.tsx src/pages/__tests__/KeymapPage.test.tsx
• npm run lint
• npm run build
• npm test -- --runInBand
• Browser demo verification: Stream toggle appears on Keymap page, enables successfully, and incoming demo notifications highlight keys.

[github-actions]

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_{Deployed from commit 3516da4}