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/en.json

@@ -31,6 +31,9 @@
   },
   "ui": {
     "language.label": "Language",
+    "language.suggest.text": "This page is also available in English.",
+    "language.suggest.cta": "Read in English",
+    "language.suggest.dismiss": "Dismiss",
     "community.title": "Join the future of privacy",
     "community.description": "SecureBit grows thanks to its community. Your ideas and feedback shape the future of secure communication - built in the open, with complete ASN.1 validation end-to-end.",
     "community.github": "GitHub Repository",
@@ -776,6 +779,28 @@
     "offline.disconnect": "Disconnect",
     "offline.learnMore": "Learn more",
     "pwa.installApp": "Install App",
-    "chat.onWeb": "You're on Web"
+    "chat.onWeb": "You're on Web",
+    "groupCall.startVoice": "Start a group voice call",
+    "groupCall.startVideo": "Start a group video call",
+    "groupCall.join": "Join",
+    "groupCall.dismiss": "Not now",
+    "groupCall.leave": "Leave call",
+    "groupCall.you": "You",
+    "groupCall.connecting": "Connecting…",
+    "groupCall.waitingLink": "Waiting for a direct link…",
+    "groupCall.legFailed": "Could not connect",
+    "groupCall.startedVoice": "{name} started a voice call",
+    "groupCall.startedVideo": "{name} started a video call",
+    "groupCall.inCall": "{count} in the call",
+    "groupCall.err.permission_denied": "The call could not start - microphone and camera access is blocked. Allow it for this site, then try again.",
+    "groupCall.err.device_not_found": "The call could not start - no microphone was found on this device.",
+    "groupCall.err.device_busy": "The call could not start - your microphone is in use by another app. Close it and try again.",
+    "groupCall.err.media_failed": "The call could not start - the microphone could not be opened.",
+    "groupCall.err.call_in_progress": "A call is already running in this group. Join it instead of starting another.",
+    "groupCall.err.not_ready": "Confirm the group code before calling.",
+    "groupCall.speaking": "{name} is speaking",
+    "groupCall.pin": "Show {name} large",
+    "groupCall.unpin": "Back to everyone",
+    "groupCall.showEveryone": "Everyone"
   }
 }