Fix Enter key omitting the selected serial line ending

[CAOShurong]

Fixes #46.

The issue report by @grbl-IO correctly identified that the Enter handler called sendText with only the text, while the Send button also passed input.endlineToSend. This makes both paths call the same function with the same two arguments, so devices requiring CR, LF, or CRLF receive the configured ending regardless of how the command is submitted.

Validation:

• npm --prefix server test covers both template handlers and the CRLF, LF, CR, and empty-ending conversions without adding dependencies. The same test passes with Node 14.21.3 on Windows x64 and Ubuntu 24.04 WSL2 x64.
• A headless VS Code-webview harness exercised the real Vue keyup and click handlers for all four endings and observed identical sendToSerial messages with no page or console errors.
• A source-level boundary harness loaded DataInputSerial.js and vscode/src/extension.ts, then used SerialPort 10.5.0's mock binding to record the final bytes written by SerialPort.write. Windows and Linux Node 14 runs matched byte-for-byte for CRLF, LF, CR, empty ending, terminator-only, and UTF-8 payload cases.
• The server packaged for node14-windows-x64; the generated executable started and served the same verified UI path.

SerialPort.list() found no active Windows port on the validation host, so no physical-device claim is made; the serial-library boundary was validated with its official mock binding.