fix: preserve remote media during renegotiation

fix: stop teacher peer-ready offer loop

fix: retry WebRTC handshake until remote media arrives

fix: harden sessions and WebRTC recovery

docs: define ui spacing polish

docs: add bugfix hardening plan

docs: define bugfix hardening design

fix(frontend): keep remote video visible before audio unlock

fix: stabilize webrtc signaling playback

fix(frontend): align start screen cards

docs(webrtc): document turn and reconnect behavior

fix(webrtc): stabilize reconnect after refresh

chore(frontend): sync package-lock with trimmed codemirror languages

docs(readme): refresh backend and frontend READMEs