fix(icom): say when a radio has no scope stream instead of drawing nothing

The CI-V trace settles it: the IC-7851 answers 27 10 01 with FB and 27 14 00
with its mode, but refuses 27 11 in BOTH shapes — it controls its scope over
CI-V and never streams it. Its last firmware is from 2016, older than the
waveform stream itself; Hamlib's caps claim otherwise, the radio is the
authority.

Rejected both ways is a permanent answer, so it is remembered and reported:
the panadapter says the radio does not send its scope, which is the one thing a
black rectangle could not say.

internal/cat/cat.go

@@ -674,6 +674,12 @@ type ScopeSweep struct {
 	LowHz  int64 `json:"low_hz"`  // left edge frequency (0 when unknown)
 	HighHz int64 `json:"high_hz"` // right edge frequency (0 when unknown)
 	Fixed  bool  `json:"fixed"`   // true = fixed-span mode, false = center-on-VFO
+	// Unsupported: this radio refuses the waveform-output command, so there will
+	// never be a sweep. The IC-7851 does — its last firmware is from 2016, older
+	// than the CI-V waveform stream — while still answering the scope's other
+	// commands. Reported so the panadapter can say so instead of showing a black
+	// rectangle that looks like a bug in OpsLog.
+	Unsupported bool `json:"unsupported"`
 }
 
 // IcomState returns the current Icom DSP state, or (zero, false) when the active