Add probe_avg_mag_sqrd_c block that taps the LPF output to measure
filtered RF power. A variable_function_probe polls it and exposes
signal_level via XML-RPC.
Display features:
- Signal strength in dB shown on tune and on 's' command
- Color-coded bar: green (strong), yellow (medium), red (weak)
- Updates after each frequency change
Signal chain now includes measurement tap:
source → LPF → demod → audio
↓
probe → var_function_probe ("signal_level")
Ryan Malloy
f6c9e465c5