Add CI and fix the Python 3.14 warnings-as-errors failure

[VirtualPaul]

Summary

The normal unit suite passes, but it cannot be imported under Python 3.14 with warnings treated as errors because a test contains an invalid escape sequence. The repository has no CI workflow to catch this or package/UI regressions.

Tested against main at fb265549480ff0d3ad8b14b28007370539b70cf3 with Python 3.14.5.

Reproduction

python3 -m unittest discover -s tests -v
# 116 tests pass, but emits SyntaxWarning at tests/test_meter.py:899

python3 -W error -m unittest discover -s tests -v
# Import fails: SyntaxError: "\\(" is an invalid escape sequence

There is also no .github/workflows directory on current main.

Suggested fix

1. Change the affected expected string to a raw string or escape the backslash ("\\\\(" as appropriate for the assertion).
2. Add GitHub Actions for supported Python versions plus the newest Python release, with warnings-as-errors on the newest job.
3. On macOS CI, compile the Swift menubar and build/expand the package.
4. Add JavaScript syntax parsing for the inline dashboard script, bash -n for shell scripts, and python -m compileall.
5. Run the 116-test suite as a required pull-request check.

Regression criteria

• python3 -W error -m unittest discover -s tests -v passes on Python 3.14.
• Every pull request runs unit, syntax, Swift compile, and package smoke checks.
• CI uploads enough logs/artifacts to diagnose a failed package build.