refactor(cluster): one rule for the filter panel

The panel had grown two shapes for the same kind of choice. Some filters were
checkboxes, some were chips, and New counties only was a checkbox duplicating a
chip - which I added, and which was the worst of it: a control that exists twice
is not more discoverable, it is one control the operator has to recognise twice.

The rule now:

  SWITCH  a behaviour that is on or off, and narrows nothing by a property of
          the station: hide worked, group duplicates, the two display options,
          LoTW users only.
  CHIPS   pick any number from a set; none picked means all. Status, mode,
          spotter continent. Selected is solid, unselected is the same chip
          faded, so the palette keeps teaching the colour code while switched
          off.

Nothing appears in both shapes. The duplicate county checkbox is gone.

Spotter continent became a chip row: seven two-letter codes fit on two lines,
they read as a set the way Status and Mode do, and several can be picked at
once - which "EU or NA" needs and a dropdown cannot express.

Both Lock buttons now sit in the heading of the section they lock, instead of
floating between sections, and every multi-select section clears the same way
through the same heading slot. One section helper and one chip helper, so the
next filter cannot drift.

The panel was also entirely hardcoded English - Search call, Hide worked, Bands,
Status - against the project's own bilingual rule. All of it goes through t()
now, both locales.

changelog.json

@@ -3,10 +3,10 @@
     "version": "0.24.4",
     "date": "",
     "en": [
-      "DX cluster: an L badge next to a callsign marks a station that uploads to LoTW, with a matching LoTW users only filter. A Spotter continent dropdown narrows the list by where the spot came FROM — a JA report on 20 m tells a European little about their own path. New counties only joins the filter panel as a second way to the NEW COUNTY chip. All of them apply to the band map too."
+      "DX cluster: an L badge next to a callsign marks a station that uploads to LoTW, with a matching LoTW users only filter, and a Spotter continent filter narrows the list by where the spot came FROM — a JA report on 20 m tells a European little about their own path. The filter panel has been tidied along one rule: a switch is a behaviour you turn on or off, chips pick any number from a set. Nothing appears in both shapes any more, the Lock buttons sit in the heading of the section they lock, every section can be cleared the same way, and the whole panel is finally translated."
     ],
     "fr": [
-      "Cluster DX : un badge L à côté de l indicatif signale une station qui utilise LoTW, avec le filtre Utilisateurs LoTW seulement qui va avec. Une liste déroulante Continent du spotter restreint selon l origine du spot — un report JA sur 20 m dit peu de chose à un Européen sur son propre chemin. Nouveaux comtés seulement rejoint le panneau de filtres, en second accès à la puce NOUV CTY. Le tout s applique aussi au bandmap."
+      "Cluster DX : un badge L à côté de l indicatif signale une station qui utilise LoTW, avec le filtre Utilisateurs LoTW seulement qui va avec, et un filtre Continent du spotter restreint selon l origine du spot — un report JA sur 20 m dit peu de chose à un Européen sur son propre chemin. Le panneau de filtres a été remis d aplomb selon une seule règle : un interrupteur est un comportement qu on active ou non, les pastilles choisissent dans un ensemble. Plus rien n existe sous les deux formes, les boutons de verrouillage sont dans le titre de la section qu ils verrouillent, chaque section s efface de la même façon, et le panneau est enfin traduit."
     ]
   },
   {