feat(groups): audio and video calls in group chats; release v6.6.6

A group call is N-1 ordinary 1:1 calls, one to each other member, each riding
the pairwise session that member already has — a transport a human already
authenticated by comparing the safety code. No mixer, no SFU, no point at which
two people's media meets anywhere but on a device.

Call control is separate from call media, because the two reach different sets
of people. Who opened a call, who joined and who left travels as group frames
signed with the sender's group identity key, so it reaches members currently
reachable only through a relay — and a relaying member can drop one but cannot
write one. Media flows only where a direct link exists, so a member without one
shows as connecting rather than being omitted. Frames carry a per-sender
sequence checked before the action, so a captured leave cannot end a later call,
and simultaneous calls converge on the lower random call id.

One capture is shared across every leg rather than one getUserMedia per member,
and legs answer without prompting: the flag permitting that is set only locally,
only while this user is in the call, and cleared when they leave.

UI: a gallery that sizes itself from the space it has, a spotlight view, an
active-speaker indicator read from the waveform, and the call surface in the
same visual language as the 1:1 one.

Also in this commit, the v6.5.0 language-suggestion work that had not been
pushed yet; its notes are in the changelog. And two fixes: the safety-code input
asks for digits rather than text, and starting a new chat from inside a group no
longer creates it behind the group where it cannot be seen — which had made it
impossible to connect to anyone new, or to add anyone to a group, while a group
was open.

Claude-Session: https://claude.ai/code/session_01XSxAkET3hQTkYDQfbjCQwZ

locales/fr.json

@@ -31,6 +31,9 @@
   },
   "ui": {
     "language.label": "Langue",
+    "language.suggest.text": "Cette page est aussi disponible en français.",
+    "language.suggest.cta": "Lire en français",
+    "language.suggest.dismiss": "Fermer",
     "community.title": "Construisez l'avenir de la vie privée",
     "community.description": "SecureBit grandit grâce à sa communauté. Vos idées et vos retours façonnent l'avenir des communications sécurisées, développées à ciel ouvert, avec une validation ASN.1 complète de bout en bout.",
     "community.github": "Dépôt GitHub",
@@ -776,7 +779,29 @@
     "offline.disconnect": "Se déconnecter",
     "offline.learnMore": "En savoir plus",
     "pwa.installApp": "Installer l'application",
-    "chat.onWeb": "Vous êtes sur la version web"
+    "chat.onWeb": "Vous êtes sur la version web",
+    "groupCall.startVoice": "Démarrer un appel vocal de groupe",
+    "groupCall.startVideo": "Démarrer un appel vidéo de groupe",
+    "groupCall.join": "Rejoindre",
+    "groupCall.dismiss": "Pas maintenant",
+    "groupCall.leave": "Quitter l'appel",
+    "groupCall.you": "Vous",
+    "groupCall.connecting": "Connexion…",
+    "groupCall.waitingLink": "En attente d'un lien direct…",
+    "groupCall.legFailed": "Connexion impossible",
+    "groupCall.startedVoice": "{name} a démarré un appel vocal",
+    "groupCall.startedVideo": "{name} a démarré un appel vidéo",
+    "groupCall.inCall": "{count} dans l'appel",
+    "groupCall.err.permission_denied": "L'appel n'a pas pu démarrer - l'accès au micro et à la caméra est bloqué. Autorisez-le pour ce site, puis réessayez.",
+    "groupCall.err.device_not_found": "L'appel n'a pas pu démarrer - aucun micro n'a été trouvé sur cet appareil.",
+    "groupCall.err.device_busy": "L'appel n'a pas pu démarrer - votre micro est utilisé par une autre application. Fermez-la et réessayez.",
+    "groupCall.err.media_failed": "L'appel n'a pas pu démarrer - le micro n'a pas pu être ouvert.",
+    "groupCall.err.call_in_progress": "Un appel est déjà en cours dans ce groupe. Rejoignez-le plutôt que d'en démarrer un autre.",
+    "groupCall.err.not_ready": "Confirmez le code du groupe avant d'appeler.",
+    "groupCall.speaking": "{name} parle",
+    "groupCall.pin": "Afficher {name} en grand",
+    "groupCall.unpin": "Revenir à tous",
+    "groupCall.showEveryone": "Tout le monde"
   },
   "manifest": {
     "name": "SecureBit.chat - Messagerie privée et chiffrée",