Introduce CI running on push to main and pull requests. Three jobs:
lint (rustfmt check + clippy with -D warnings), test (build and test the
workspace with --locked), and REUSE compliance. Installs the required
system libraries (opus, alsa, soapysdr) and caches the cargo registry
and target directory.
Assisted-By: Claude Code (claude-opus-4)
Claude-Session: https://claude.ai/code/session_01NFpGtGTWUEYXLwZeZs2RAV
Signed-off-by: Stan Grams <sjg@haxx.space>
