feat(cluster): Chase New — a panel for what is new and audible here

PSK Reporter tells you what is actually being decoded in your region, which
is a larger set than what somebody chose to spot: nobody spots the FT8 caller
running ten watts from a rare square.

Almost all of it existed. The MQTT payload already carries frequency, mode,
transmitter and both grids; the watcher already drops any report collected
further than NearKm from the operator, which is exactly the question worth
asking — the station is being heard HERE, not in Japan; and with grid chasing
on the subscription is already every band, filtered at the broker by receiver
square, measured at 0.2 to 1.2 messages a second. This reads messages that
were arriving and being discarded.

"New" is not decided here. Every spot goes through ClusterSpotStatuses, the
same function the DX cluster grid uses and the same cached index, so the two
panels cannot drift apart the way the county columns did. Cost per message is
map lookups behind an option cached in an atomic, because the MQTT goroutine
must never wait on the settings store.

The option is its own, not nested under grid chasing: chasing squares and
chasing entities are different wants, and the feed now has three consumers,
any one of which brings it up and none of which cuts the others loose when it
goes down.

The panel says "digital modes only" in its footer. An empty list has to mean
"nothing new on FT8/FT4/JS8 near you", not "the band is dead" — it will never
show a new entity on CW.

changelog.json

@@ -4,11 +4,13 @@
     "date": "",
     "en": [
       "Send Spot: the comment now carries the award references after the mode — the ones you assigned (POTA, SOTA, IOTA…), not the DXCC, zone and prefix every reader works out from the callsign. A self-spot carries your OWN activation references instead.",
-      "Modes: a fresh install now starts with SSB, CW, FT8, FT4, FT2, RTTY, PSK31 and FM. AM and DIGITALVOICE stay in the available list but are no longer selected by default."
+      "Modes: a fresh install now starts with SSB, CW, FT8, FT4, FT2, RTTY, PSK31 and FM. AM and DIGITALVOICE stay in the available list but are no longer selected by default.",
+      "Chase new: a panel listing the stations PSK Reporter is hearing within about 300 km of you that are new against your log — entity, band, mode, slot, prefix or square. Click one to put it in the entry and tune the rig. Digital modes only, and it shares the feed the band-opening watch and the locator store already use."
     ],
     "fr": [
       "Envoi de spot : le commentaire porte désormais les références de diplôme après le mode — celles que vous avez attribuées (POTA, SOTA, IOTA…), pas le DXCC, la zone et le préfixe que chacun déduit de l’indicatif. Un auto-spot porte VOS références d’activation.",
-      "Modes : une installation neuve démarre avec SSB, CW, FT8, FT4, FT2, RTTY, PSK31 et FM. AM et DIGITALVOICE restent dans la liste disponible mais ne sont plus sélectionnés par défaut."
+      "Modes : une installation neuve démarre avec SSB, CW, FT8, FT4, FT2, RTTY, PSK31 et FM. AM et DIGITALVOICE restent dans la liste disponible mais ne sont plus sélectionnés par défaut.",
+      "Chasse au nouveau : un panneau listant les stations que PSK Reporter entend à moins de 300 km de chez vous et qui sont nouvelles par rapport à votre log — entité, bande, mode, créneau, préfixe ou carré. Un clic la met en saisie et accorde la radio. Modes numériques uniquement, et le flux est partagé avec la veille d’ouvertures et la base des locators."
     ]
   },
   {