- Assert DTR/RTS after serial port open to prevent wireless modules
(HC-12/HC-15/Bluetooth bridges) from entering AT command mode after
the unavoidable Linux kernel DTR pulse on every open() call.
- Add dtr/rts fields to TransportConfig::Serial (default: false).
- Add set_dtr()/set_rts() on SerialTransport, Connection, SessionHandle.
- Add SessionCmd::SetDtr/SetRts for live toggling via command channel.
- Add DTR/RTS checkboxes to GUI session controls (visible when connected)
and to config form for persistence.
- Add test_plot_serial.c and test_text_serial.c — standalone C test
tools for sending MixedTextPlot frames and plain text over serial.
- Update AGENTS.md with build prerequisites, architecture map, testing
conventions, env vars, and known quirks.
