Align root, Software, and Firmware READMEs with security, CI, web UI, blob policy, and six-band EQ details.
Co-authored-by: Cursor <cursoragent@cursor.com>
Expand local-only firmware README, add check_si4684_blobs.py to verify gitignore and clean history, and gate main with a new si4684-blobs workflow job.
Co-authored-by: Cursor <cursoragent@cursor.com>