fix reading find refocus

[kennyyennk]

Summary

• refocus and select the reading-mode find input when Cmd/Ctrl+F is pressed while the find bar is already open
• keep the existing open-on-first-press behavior unchanged

Testing

• bun test
• bun run build
• cargo check --release --manifest-path src-tauri/Cargo.toml

[mattenarle10]

thanks for this. clean small fix for the reading find refocus flow, and local checks pass on my side.