feat(hrdlog): ON AIR — publish the live frequency, mode and rig

Puts "F4BPO is on air 14,074,000 FT8 IC-7300" on hrdlog.net's front page while
the station is operating, which is what HRDLog's own "Automatic HRDLog ON AIR"
setting does.

The endpoint and its field names come from HRDLog's own library
(github.com/iw1qlh/HRDLOG-net-library, HrdProtocol.SendOnAirAsync): OnAir.aspx,
with Frequency in Hz, Mode, Radio, Callsign, Code and App. Read rather than
guessed — an invented endpoint would have produced a switch that silently did
nothing.

HTTPS where that library uses plain HTTP: the upload code is a credential and
has no business crossing the network in clear, and the sibling NewEntry
endpoint on the same host already serves TLS.

A heartbeat every two minutes, not a change notification — HRDLog drops a
station from the list when it stops hearing from it. Silent when switched off,
unconfigured, or when the rig reports no frequency: announcing 0 Hz would say
the operator is on air on nothing. Failures are logged, never toasted; a
broadcast the operator did not ask for at that instant must not interrupt them
every two minutes on a flaky link.

Its own switch beside auto-upload rather than folded into it: this is a live
status and needs the rig readable, not a QSO.

changelog.json

@@ -8,7 +8,8 @@
       "Call lookup: QRZ.com now fills Name with the first name only, and optionally with the operator nickname instead.",
       "Entry form: a narrower left column, State beside the locator, and a new line with County, CQ, ITU and DXCC.",
       "Station Control: the short and long path headings are repeated under the compass, at a readable size and clickable.",
-      "Compact mode: the window now fits the entry strip instead of leaving a band of empty space below it."
+      "Compact mode: the window now fits the entry strip instead of leaving a band of empty space below it.",
+      "HRDLog: an ON AIR option publishes your live frequency, mode and rig on hrdlog.net."
     ],
     "fr": [
       "Cluster : « Masquer les contactés » ne masque plus un spot qui est un nouveau préfixe, comté, carré ou parc dans une contrée déjà faite.",
@@ -16,7 +17,8 @@
       "Recherche d indicatif : QRZ.com remplit désormais Nom avec le seul prénom, et au choix avec le surnom de l opérateur.",
       "Saisie : colonne de gauche plus étroite, État à côté du locator, et une nouvelle ligne Comté, CQ, ITU et DXCC.",
       "Contrôle station : les azimuts court et long chemin sont repris sous la boussole, lisibles et cliquables.",
-      "Mode compact : la fenêtre épouse la bande de saisie au lieu de laisser une bande vide en dessous."
+      "Mode compact : la fenêtre épouse la bande de saisie au lieu de laisser une bande vide en dessous.",
+      "HRDLog : une option ON AIR publie ta fréquence, ton mode et ta radio en direct sur hrdlog.net."
     ]
   },
   {