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.

frontend/src/lib/i18n.tsx

@@ -270,7 +270,7 @@ const en: Dict = {
   'clu.muteWorkedHint': '(they stay in the list, just quiet — leaves the colour for what is left to do)',
   'clu.slotHighlight': 'Colour the stations not worked on this band and mode',
   'clu.slotHighlightHint': '(by callsign, whatever the entity status says)',
-  'clu.workedSameSlot': 'Already worked only on the same slot',
+  'bo.enable': 'Watch for band openings', 'bo.enableHint': '(10, 12, 6, 4 and 2 m. Switching this on adds the two RBN nodes and subscribes to the PSK Reporter feed — the detection needs far more ears than a cluster can give it.)', 'bo.feedUp': 'PSK Reporter feed up — {n} decodes seen', 'bo.feedDown': 'PSK Reporter feed down — needs your station grid, and a moment to connect', 'clu.workedSameSlot': 'Already worked only on the same slot',
   'clu.workedSameSlotHint': '— a spot shows "worked" only if you worked that call on the SAME band and mode, not just anywhere. Combines with digital-mode grouping (Settings → General): with it on, a call worked on 20m FT8 also counts as worked for a 20m FT4 spot; with it off, FT8 and FT4 are separate slots.',
   // Backup panel
   'bk.hintMysql': 'On close (once/day) OpsLog snapshots the local SQLite (config) AND exports the shared MySQL log to ADIF — opslog-log-<date>.adi — so your contacts are protected even though they live on the server. Rotation keeps the last N of each.',
@@ -690,7 +690,7 @@ const fr: Dict = {
   'clu.muteWorkedHint': '(elles restent dans la liste, simplement discrètes — la couleur reste pour ce qui est à faire)',
   'clu.slotHighlight': 'Colorer les stations non contactées sur cette bande et ce mode',
   'clu.slotHighlightHint': "(par indicatif, quel que soit le statut de l'entité)",
-  'clu.workedSameSlot': 'Déjà contacté seulement sur le même slot',
+  'bo.enable': 'Surveiller les ouvertures de bande', 'bo.enableHint': "(10, 12, 6, 4 et 2 m. Activer ajoute les deux nœuds RBN et souscrit au flux PSK Reporter — la détection a besoin de bien plus d oreilles qu un cluster ne peut en fournir.)", 'bo.feedUp': 'Flux PSK Reporter actif — {n} décodages vus', 'bo.feedDown': 'Flux PSK Reporter inactif — il faut ton locator, et un instant pour se connecter', 'clu.workedSameSlot': 'Déjà contacté seulement sur le même slot',
   'clu.workedSameSlotHint': '— un spot n\'affiche « contacté » que si vous avez contacté cet indicatif sur la MÊME bande et le MÊME mode, pas juste n\'importe où. Se combine avec le groupage des modes numériques (Réglages → Général) : activé, un indicatif contacté en 20m FT8 compte aussi comme contacté pour un spot 20m FT4 ; désactivé, FT8 et FT4 sont des slots distincts.',
   'bk.hintMysql': "À la fermeture (1×/jour) OpsLog sauvegarde le SQLite local (config) ET exporte le log MySQL partagé en ADIF — opslog-log-<date>.adi — pour protéger tes contacts même s'ils sont sur le serveur. La rotation garde les N derniers de chaque.",
   'bk.hint': "OpsLog peut copier la base SQLite dans un dossier de ton choix à la fermeture, une fois par jour. La rotation garde les N dernières copies et supprime les plus anciennes.",