feat(cluster): quiet the worked spots, light up the empty slots

Two options that change what the eye is pulled towards, both applying to the
cluster list AND the band map.

Mute worked before: a spot that brings nothing new loses its colour and its
badges. It stays in the list - the operator asked for less noise, not less
information. "Brings nothing new" reuses the dimming rule the cluster list
already had rather than inventing a second notion of done, so it keeps obeying
the same-slot option and the digital-mode grouping for free. A new-band or
new-slot status is NOT muted: having worked that callsign once on another band
says nothing about the band in front of you.

Highlight unworked in this slot: colours any callsign not yet worked on this
band and this mode, whatever the entity says. For an operator filling slots a
common entity on a fresh band+mode is the whole point, and the entity-level
status flatly calls it worked. It reuses the existing new-slot status, so no new
colour, no new legend, no new badge - both panels already knew how to draw it.

WorkedSlot is computed independently of the same-slot preference: it is what
this option reads, and it must not change meaning because a different option was
toggled. The slot index is now built when either option needs it, and the status
cache is keyed on both so a toggle invalidates it.

The rules live in one module used by both panels. Marker colours already taught
us what happens when the two derive the same thing separately.

changelog.json

@@ -3,10 +3,12 @@
     "version": "0.24.3",
     "date": "",
     "en": [
-      "Band openings: OpsLog now tells you when 6, 4 or 2 m opens. It watches the spots already arriving from your clusters and RBN — several different stations appearing at single-hop range (500–2400 km) in the same bearing sector within a few minutes is the signature of sporadic E, and nothing else looks like it. You get one message per band per opening, naming the sector and the typical distance. An opening outside the usual season is still announced, and flagged as unusual: those are the ones worth knowing about. Nothing to configure — but the quality depends on having a cluster or RBN feed carrying VHF spots, and 2 m openings are often worked without ever being spotted."
+      "Band openings: OpsLog now tells you when 6, 4 or 2 m opens. It watches the spots already arriving from your clusters and RBN — several different stations appearing at single-hop range (500–2400 km) in the same bearing sector within a few minutes is the signature of sporadic E, and nothing else looks like it. You get one message per band per opening, naming the sector and the typical distance. An opening outside the usual season is still announced, and flagged as unusual: those are the ones worth knowing about. Nothing to configure — but the quality depends on having a cluster or RBN feed carrying VHF spots, and 2 m openings are often worked without ever being spotted.",
+      "DX cluster, two display options (Settings › DX cluster). The first drops the colour and the badges on stations you have already worked: they stay in the list, they simply stop competing for your attention. The second colours every callsign you have not worked on this band and this mode, even when the entity itself is long since confirmed — the view for filling slots rather than chasing new ones. Both apply to the cluster list and to the band map, so the two panels always agree."
     ],
     "fr": [
-      "Ouvertures de bande : OpsLog te signale désormais l ouverture du 6, du 4 ou du 2 m. Il surveille les spots qui arrivent déjà de tes clusters et du RBN — plusieurs stations différentes apparaissant à distance de saut simple (500–2400 km) dans le même secteur d azimut en quelques minutes, c est la signature de l Es, et rien d autre n y ressemble. Un message par bande et par ouverture, avec le secteur et la distance typique. Une ouverture hors saison est annoncée quand même, et signalée comme inhabituelle : ce sont celles qu il ne faut surtout pas manquer. Rien à configurer — mais la qualité dépend d avoir un flux cluster ou RBN qui porte des spots VHF, et les ouvertures 2 m sont souvent travaillées sans jamais être spottées."
+      "Ouvertures de bande : OpsLog te signale désormais l ouverture du 6, du 4 ou du 2 m. Il surveille les spots qui arrivent déjà de tes clusters et du RBN — plusieurs stations différentes apparaissant à distance de saut simple (500–2400 km) dans le même secteur d azimut en quelques minutes, c est la signature de l Es, et rien d autre n y ressemble. Un message par bande et par ouverture, avec le secteur et la distance typique. Une ouverture hors saison est annoncée quand même, et signalée comme inhabituelle : ce sont celles qu il ne faut surtout pas manquer. Rien à configurer — mais la qualité dépend d avoir un flux cluster ou RBN qui porte des spots VHF, et les ouvertures 2 m sont souvent travaillées sans jamais être spottées.",
+      "Cluster DX, deux options d affichage (Paramètres › Cluster DX). La première enlève la couleur et les badges sur les stations déjà contactées : elles restent dans la liste, elles cessent simplement d attirer l œil. La seconde colore tout indicatif non contacté sur cette bande et ce mode, même si l entité est confirmée depuis longtemps — la vue pour remplir des slots plutôt que pour chasser du nouveau. Les deux s appliquent à la liste cluster et au bandmap, les deux panneaux restent donc cohérents."
     ]
   },
   {