fix: omit missing baud rate from send placeholder

[AysajanE]

Summary

Avoid rendering the literal word undefined when a selected serial port has no baud rate.

Change

• packages/webviews/monitor-shared/src/serial-monitor/MonitorSendBar.jsx
• packages/webviews/monitor/src/features/app/MonitorSendBar.test.jsx

Checks

• NODE_OPTIONS="--import=data:text/javascript,globalThis.__dirname=process.cwd()" npm --prefix packages/webviews/monitor test -- --configLoader runner --run src/features/app/MonitorSendBar.test.jsx — passed in a network-isolated container.

Fixes #26

---

AI assistance was used; I reviewed and own this change.

Verification

Northset proof-of-pass receipt M-160
Contributor self-run; not maintainer verification.

[AysajanE]

The only failing validate check appears to be an infrastructure error: amannn/action-semantic-pull-request received GitHub’s “Unicorn” HTML error page. I could not find a source or PR-title validation failure in the job log.

Could a maintainer please rerun that check when convenient? If the rerun reports an actionable problem, I’ll address it.

[AysajanE]

The PR-title check appears to have failed on a transient GitHub API error rather than the title: the semantic-title action received GitHub's Unicorn! HTML error page, while the title is fix: omit missing baud rate from send placeholder. Could a maintainer rerun that check?