feat(bandopen): read PSK Reporter, and arrange the sources the watch needs

The detection shipped reading whatever the operator's cluster nodes happened to
carry. On VHF that is a few hundred skimmers, nearly all of them on HF: a 6 m
opening carrying 869 stations reached OpsLog as a handful of spots or none, and
Nexus flagged it on the same PC while OpsLog stayed silent.

internal/pskr subscribes to pskr/filter/v2/<band>/# on PSK Reporter's MQTT
broker. Every ordinary station running WSJT-X reports what it decodes, so the
difference is two orders of magnitude rather than a threshold. The feed's shape
suits us exactly: BOTH grids are in each message, so distance and bearing are
arithmetic — no lookup, and no DXCC-centre approximation, which is what made the
cluster path's bearings coarse. The geometry is injected from app.go so it stays
the same arithmetic the cluster path uses; two answers to one question is how a
bearing quietly becomes wrong.

Volume was the design constraint, not the protocol. Six metres open is thousands
of messages a minute and this runs on some very old PCs, so nothing is kept or
persisted in the watcher: each message is parsed, measured and handed on or
dropped, and the detector's existing window does the deciding.

And the part that was the real bug: enabling the watch now ARRANGES ITS OWN
SOURCES. It adds the two RBN nodes when missing and brings the feed up. A
feature that silently depends on sources nobody can know are needed does not
look unconfigured, it looks broken. Matched on host and port, not name, so an
operator who renamed theirs does not get a duplicate — which the detector would
read as twice as many stations, and announce an opening that is not there.

Turning it off leaves the nodes alone: they may have been wanted for their own
sake, and removing a node someone is using is worse than leaving one they are not.

changelog.json

@@ -7,14 +7,16 @@
       "CW over CAT now works on a Kenwood. The KY command was sent in Elecraft's variable-length form; a Kenwood needs exactly 24 characters, so every message was refused.",
       "Shared CAT is steadier and now diagnoses itself. It survives a rig answering \"busy\" just after transmit instead of dropping the link, stops repeating a PTT state the client never changed, and logs a plain explanation when another program has taken its port or when a client is set to a rig model instead of Hamlib NET rigctl. It also answers the lock-mode and stop-morse commands some clients send around every transmit, instead of refusing them.",
       "Web publishing now offers every field a QSO carries, awards included — 123 instead of 23 — from a searchable dropdown, with the chosen columns listed above it in publication order. Choose carefully: the page is public and the list includes addresses and e-mail.",
-      "Band-opening detection no longer ignores long paths. It capped them at 2400 km on the assumption that anything further was not a single hop; multi-hop sporadic E is ordinary on 6 m, so the openings most worth hearing about were the ones being discarded. Direction still decides — a second hop leaves the sector the first one entered."
+      "Band-opening detection no longer ignores long paths. It capped them at 2400 km on the assumption that anything further was not a single hop; multi-hop sporadic E is ordinary on 6 m, so the openings most worth hearing about were the ones being discarded. Direction still decides — a second hop leaves the sector the first one entered.",
+      "Band-opening detection now has the data it needs. Switching on \"Watch for band openings\" (Settings › DX Cluster) subscribes to the PSK Reporter feed — every station on the air reporting what it decodes, rather than the handful of VHF spots a cluster carries — and adds the two RBN nodes if they are missing. Pick the bands to watch: 12, 10, 6, 4 and 2 m."
     ],
     "fr": [
       "Décodes digitaux : le carré locator d une station pouvait être enregistré comme son indicatif quand le texte du message sortait de l ordinaire. Un grid à la place de l indicatif est maintenant refusé.",
       "Le CW par CAT fonctionne sur Kenwood. La commande KY partait sous la forme Elecraft à longueur libre ; un Kenwood exige exactement 24 caractères, donc chaque message était refusé.",
       "Le CAT partagé est plus solide et se diagnostique tout seul. Il survit à un rig qui répond « occupé » juste après une émission au lieu de lâcher le lien, cesse de répéter un état PTT que le client n a pas changé, et écrit une explication claire quand un autre programme lui a pris son port ou qu un client est réglé sur un modèle de rig au lieu de Hamlib NET rigctl. Il répond aussi aux commandes de verrouillage et d arrêt du morse que certains logiciels envoient à chaque émission, au lieu de les refuser.",
       "La publication web propose désormais tous les champs d un QSO, awards compris — 123 au lieu de 23 — depuis une liste déroulante cherchable, les colonnes choisies étant listées au-dessus dans l ordre de publication. À choisir avec soin : la page est publique et la liste contient adresses et e-mails.",
-      "La détection d ouverture n ignore plus les longues distances. Elle plafonnait à 2400 km en supposant qu au-delà ce n était plus un saut simple ; l Es à sauts multiples est ordinaire sur 6 m, donc les ouvertures les plus intéressantes étaient précisément celles qu on jetait. C est toujours la direction qui tranche — un second saut repart dans le secteur où le premier est arrivé."
+      "La détection d ouverture n ignore plus les longues distances. Elle plafonnait à 2400 km en supposant qu au-delà ce n était plus un saut simple ; l Es à sauts multiples est ordinaire sur 6 m, donc les ouvertures les plus intéressantes étaient précisément celles qu on jetait. C est toujours la direction qui tranche — un second saut repart dans le secteur où le premier est arrivé.",
+      "La détection d ouverture dispose enfin des données qu il lui faut. Activer « Surveiller les ouvertures de bande » (Paramètres › Cluster DX) souscrit au flux PSK Reporter — toutes les stations en l air qui rapportent ce qu elles décodent, au lieu des quelques spots VHF que porte un cluster — et ajoute les deux nœuds RBN s ils manquent. Les bandes surveillées se choisissent : 12, 10, 6, 4 et 2 m."
     ]
   },
   {