fix(relays): {value} is the relay's label, not a per-relay value

It was built the other way round on a misreading of two screenshots: the pattern
held {value} and the per-relay boxes held numbers to drop into it. The ask was
simpler and better — {value} is the name typed in Relay labels, so a switch
addressed by antenna name is one pattern instead of eight URLs:

  http://10.10.10.100/relay?on={value}   relay 1 named Ant1  →  ?on=Ant1

Renaming the antenna re-addresses it, and the name on the button and the name on
the wire cannot drift apart because they are the same string. It works in the
per-relay URLs and in the patterns alike, so the per-relay boxes go back to
holding URLs and nothing about them changes meaning any more.

The label is percent-encoded with %20 rather than "+" for a space: "+" is a
space only in a query string and a literal plus in a path, and this can land in
either half of a URL.

{value} on a relay with no label would send "?on=", an empty parameter that most
boards answer with a cheerful 200 and no movement. The driver refuses it and
names the label as what is missing; the editor warns while it is being typed,
beside the empty box rather than after an antenna fails to switch. The labels
also join the driver's cache key — they are part of the wire format now.

changelog.json

@@ -6,13 +6,13 @@
       "WinKeyer: the opening probe goes out as one write, matching a capture of a client that talks to the same K3NG keyer, and the handshake bytes are always logged so a keyer that stays silent can be diagnosed.",
       "DX cluster: when spots arrive and every one is filtered out, the panel says so, names the filters doing it and offers to clear them — it used to say “waiting for spots” beside a counter reading 76 live.",
       "DX cluster: the log times the connection and the first spot, so a slow first launch can be told apart from a quiet node.",
-      "Generic HTTP relay: its URLs were never actually sent — fixed. Adds {value} and {relay-1}, https, and no host or test needed."
+      "Generic HTTP relay: its URLs were never actually sent — fixed. {value} sends the relay's label, {relay-1} counts from zero, no host needed."
     ],
     "fr": [
       "WinKeyer : la sonde d’ouverture part en un seul envoi, calquée sur la capture d’un client qui dialogue avec le même manipulateur K3NG, et les octets de la poignée de main sont toujours journalisés pour diagnostiquer un manipulateur muet.",
       "Cluster DX : quand des spots arrivent et que tout est filtré, le panneau le dit, nomme les filtres responsables et propose de les effacer — il affichait « en attente de spots » à côté d’un compteur à 76 en direct.",
       "Cluster DX : le journal chronomètre la connexion et le premier spot, pour distinguer un premier lancement lent d’un nœud silencieux.",
-      "Relais HTTP générique : ses URL n’étaient jamais envoyées — corrigé. Ajoute {value} et {relay-1}, https, sans hôte ni test."
+      "Relais HTTP générique : ses URL n’étaient jamais envoyées — corrigé. {value} envoie le libellé du relais, {relay-1} compte de zéro, hôte inutile."
     ]
   },
   {