feat(cluster): self-spot on the master node while logging

Settings -> DX Cluster: a toggle and an interval. When it is on, logging a QSO
announces the station on the master cluster — the QSO's own station callsign as
the DX, on the frequency the contact was made on — so callers find the run
without waiting for someone else to spot it. The node fills the DE field from
the login, so the spotter is us too: a self-spot.

It fires on the FIRST QSO of a frequency and then at most once per interval.
Both halves matter: announcing every QSO would flood the node and get the
station filtered out, while a pure timer would stay silent for minutes after a
band change. A drift of up to 500 Hz still counts as the same run, so nudging
the VFO mid-pileup does not re-announce.

Five minutes is the floor, clamped in SaveSelfSpotSettings as well as in the
input: the limit protects the node from us, so it must not depend on the
frontend. The interval input keeps raw text and clamps on blur — clamping per
keystroke rewrote "10" to "5" as soon as the "1" landed.

Wired into both log paths (manual entry and UDP auto-log) on the async side, so
a cluster that is slow or down never holds up logging. A send failure restores
the previous throttle state, so the next QSO retries instead of sitting out an
interval that produced no spot.

frontend/wailsjs/go/models.ts

@@ -2914,6 +2914,20 @@ export namespace main {
 	        this.unlocked = source["unlocked"];
 	    }
 	}
+	export class SelfSpotSettings {
+	    enabled: boolean;
+	    minutes: number;
+	
+	    static createFrom(source: any = {}) {
+	        return new SelfSpotSettings(source);
+	    }
+	
+	    constructor(source: any = {}) {
+	        if ('string' === typeof source) source = JSON.parse(source);
+	        this.enabled = source["enabled"];
+	        this.minutes = source["minutes"];
+	    }
+	}
 	export class SpotQuery {
 	    call: string;
 	    band: string;