feat: relay auto-control by frequency / band (PstRotator-style)

Automatically switches the Station Control relay boards from the rig's
current frequency / band. Each relay carries one rule: off (manual), a
frequency window (ON inside [lo,hi] kHz, OFF outside), or a set of bands
(ON on those bands, OFF elsewhere). Evaluated on every CAT frequency/band
change; a relay is only switched when its desired state actually changed,
so tuning within a range doesn't hammer the board.

A cached atomic flag keeps the CAT hot path a no-op when the feature is off
(important during FT8 slice churn). Saving re-applies from the live
frequency so a changed rule takes effect immediately.

New Settings → Hardware → Relay auto-control section: master enable plus a
per-relay mode (Off / Frequency / Band) with kHz range inputs or band
chips, per configured relay board. i18n EN + FR. Azimuth/Time modes (the
other two PstRotator tabs) are left for later.

app.go

@@ -484,6 +484,9 @@ type App struct {
 	pttMu          sync.Mutex
 	udpLogMu       sync.Mutex      // serialises UDP auto-log so concurrent packets can't both pass the dedup check
 	adifMonMu      sync.Mutex      // guards the ADIF-monitor config (file list + per-file read offsets)
+	relayAutoMu    sync.Mutex        // serialises relay auto-control evaluation
+	relayAutoLast  map[string]bool   // deviceID|relay → last applied on/off, so we only switch on a real change
+	relayAutoOn    atomic.Bool       // cached "auto-control enabled" so the CAT hot path skips work when off
 	pttPort        serial.Port     // open serial port while PTT (RTS/DTR) is asserted
 	pttKeyedMethod string          // "cat" | "rts" | "dtr" while keyed; "" when idle
 	pttGen         int64           // bumped on every key; a delayed unkey only fires if unchanged (guards against a stale release cutting a new transmission)
@@ -810,6 +813,7 @@ func (a *App) startup(ctx context.Context) {
 	a.qso = qso.NewRepo(logbookConn)
 	go a.rebuildWorkedIndex() // in-memory worked-index for per-spot alert checks
 	go a.adifMonitorLoop()    // watch external ADIF files (fldigi, N1MM…) for new QSOs
+	a.relayAutoOn.Store(a.GetRelayAuto().Enabled) // prime the relay auto-control hot-path flag
 
 	// cty.dat for offline DXCC / country resolution. Cached on disk; first
 	// run downloads it from country-files.com in the background so startup
@@ -895,6 +899,13 @@ func (a *App) startup(ctx context.Context) {
 			wruntime.EventsEmit(a.ctx, "cat:state", s)
 		}
 		a.emitRadioUDP(s)
+		// Drive station relays by the current frequency/band (PstRotator-style
+		// automatic control). Cheap cached-flag check keeps this a no-op when the
+		// feature is off; when on, run off this callback so a slow relay board never
+		// stalls rig-state processing.
+		if a.relayAutoOn.Load() {
+			go a.applyRelayAuto(s.FreqHz, s.Band)
+		}
 	})
 	a.reloadCAT()