feat(theme): four themes with an actual hue — Indigo, Ocean, Plum, Nordic

The seven existing themes are warm beige, cool grey, sage grey, slate, warm
dark, graphite and black — every one neutral, six of the seven accented orange.
Picking a theme changed the shade of grey and little else.

These colour the SURFACES, not just the accent, and each takes a different
primary so the picker tells them apart at a glance: violet on deep indigo, cyan
on deep teal, magenta on aubergine, indigo on a crisp cool white.

The semantic colours stay recognisable as themselves. A logger is read for
hours and "red means a problem" cannot become a decorative choice, so the hue
budget went on the surfaces and the primary. Where a theme's primary would have
collided with a meaning, the MEANING kept its identity and the ornament moved:
Ocean's info is blue rather than cyan, Plum's danger is red rather than rose,
and the matrix entity ramp shifts to cyan under Indigo and teal under Nordic so
a "confirmed" cell never reads as a button.

Everything else follows for free: the grids resolve var(--…) at runtime, so
they re-skin with no re-render. The three shared registrations that do NOT
follow automatically are done — the chart palette (light vs dark ramp) and the
date-picker icon inversion, which is keyed on an explicit list of dark themes.

frontend/src/lib/i18n.tsx

@@ -108,8 +108,8 @@ const en: Dict = {
   'settings.pane.recent': 'Recent QSOs', 'settings.pane.netcontrol': 'Net control',
   'settings.pane.flex': 'Flex Console', 'settings.pane.icom': 'Icom Console', 'settings.pane.yaesu': 'Yaesu Console', 'yaesu.notConnected': 'Yaesu CAT not connected', 'yaesu.meters': 'Meters', 'yaesu.bandMode': 'Band & mode', 'yaesu.receive': 'Receive', 'yaesu.noiseFilter': 'Noise & filter', 'yaesu.transmit': 'Transmit', 'yaesu.refresh': 'Refresh', 'yaesu.tuneHint': 'Start an antenna-tuner cycle', 'yaesu.sToRst': 'Click to fill the RST sent', 'yaesu.sidebandHint': 'Click to select this mode; click again to switch sideband (U/L)', 'yaesu.splitUpHint': 'Transmit this far above the receive frequency, and turn split on', 'yaesu.txOn': 'TX', 'yaesu.cw': 'CW', 'yaesu.breakInHint': 'Break-in: the rig switches to receive between characters', 'yaesu.zinHint': 'Zero-in: retune so the station you hear lands on your CW pitch',
   'theme.auto': 'Auto (system)', 'theme.light-warm': 'Warm light', 'theme.light-cool': 'Cool light',
-  'theme.light-sage': 'Sage light', 'theme.dim-slate': 'Dim slate', 'theme.dark-warm': 'Warm dark',
-  'theme.dark-graphite': 'Graphite dark', 'theme.high-contrast': 'High contrast',
+  'theme.light-sage': 'Sage light', 'theme.light-nordic': 'Nordic light', 'theme.dim-slate': 'Dim slate', 'theme.dark-warm': 'Warm dark',
+  'theme.dark-graphite': 'Graphite dark', 'theme.dark-indigo': 'Indigo', 'theme.dark-teal': 'Ocean', 'theme.dark-plum': 'Plum', 'theme.high-contrast': 'High contrast',
   // Settings navigation (sidebar groups + section names)
   'nav.user': 'User Configuration', 'nav.software': 'Software Configuration', 'nav.hardware': 'Hardware Configuration', 'nav.lists': 'Lists',
   'sec.station': 'Station Information', 'sec.profiles': 'Profiles', 'sec.operating': 'Operating conditions',
@@ -532,8 +532,8 @@ const fr: Dict = {
   'settings.pane.recent': 'QSO récents', 'settings.pane.netcontrol': 'Gestion de net',
   'settings.pane.flex': 'Flex Console', 'settings.pane.icom': 'Icom Console', 'settings.pane.yaesu': 'Yaesu Console', 'yaesu.notConnected': 'CAT Yaesu non connecté', 'yaesu.meters': 'Mesures', 'yaesu.bandMode': 'Bande et mode', 'yaesu.receive': 'Réception', 'yaesu.noiseFilter': 'Bruit et filtre', 'yaesu.transmit': 'Émission', 'yaesu.refresh': 'Actualiser', 'yaesu.tuneHint': "Lancer un cycle d'accord d'antenne", 'yaesu.sToRst': 'Cliquer pour remplir le RST envoyé', 'yaesu.sidebandHint': 'Cliquer pour choisir ce mode ; recliquer pour changer de bande latérale (U/L)', 'yaesu.splitUpHint': "Émettre à cette distance au-dessus de la fréquence de réception, et activer le split", 'yaesu.txOn': 'TX', 'yaesu.cw': 'CW', 'yaesu.breakInHint': "Break-in : la radio repasse en réception entre les caractères", 'yaesu.zinHint': "Zéro-in : réaccorde pour que la station entendue tombe sur votre note CW",
   'theme.auto': 'Auto (système)', 'theme.light-warm': 'Clair chaud', 'theme.light-cool': 'Clair froid',
-  'theme.light-sage': 'Clair sauge', 'theme.dim-slate': 'Ardoise tamisé', 'theme.dark-warm': 'Sombre chaud',
-  'theme.dark-graphite': 'Sombre graphite', 'theme.high-contrast': 'Contraste élevé',
+  'theme.light-sage': 'Clair sauge', 'theme.light-nordic': 'Clair nordique', 'theme.dim-slate': 'Ardoise tamisé', 'theme.dark-warm': 'Sombre chaud',
+  'theme.dark-graphite': 'Sombre graphite', 'theme.dark-indigo': 'Indigo', 'theme.dark-teal': 'Océan', 'theme.dark-plum': 'Prune', 'theme.high-contrast': 'Contraste élevé',
   'nav.user': 'Configuration utilisateur', 'nav.software': 'Configuration logicielle', 'nav.hardware': 'Configuration matérielle', 'nav.lists': 'Listes',
   'sec.station': 'Informations station', 'sec.profiles': 'Profils', 'sec.operating': "Conditions d'opération",
   'sec.confirmations': 'Confirmations', 'sec.external': 'Services externes',