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/de.json

@@ -36,6 +36,9 @@
   },
   "ui": {
     "language.label": "Sprache",
+    "language.suggest.text": "Diese Seite gibt es auch auf Deutsch.",
+    "language.suggest.cta": "Auf Deutsch lesen",
+    "language.suggest.dismiss": "Schließen",
     "community.title": "Gestalten Sie die Zukunft der Privatsphäre mit",
     "community.description": "SecureBit wächst durch seine Community. Ihre Ideen und Ihr Feedback prägen die Zukunft sicherer Kommunikation - offen entwickelt, mit vollständiger ASN.1-Validierung von Ende zu Ende.",
     "community.github": "GitHub-Repository",
@@ -781,6 +784,28 @@
     "offline.disconnect": "Trennen",
     "offline.learnMore": "Mehr erfahren",
     "pwa.installApp": "App installieren",
-    "chat.onWeb": "Sie nutzen die Web-Version"
+    "chat.onWeb": "Sie nutzen die Web-Version",
+    "groupCall.startVoice": "Gruppen-Sprachanruf starten",
+    "groupCall.startVideo": "Gruppen-Videoanruf starten",
+    "groupCall.join": "Beitreten",
+    "groupCall.dismiss": "Jetzt nicht",
+    "groupCall.leave": "Anruf verlassen",
+    "groupCall.you": "Du",
+    "groupCall.connecting": "Verbinden…",
+    "groupCall.waitingLink": "Warten auf eine direkte Verbindung…",
+    "groupCall.legFailed": "Verbindung fehlgeschlagen",
+    "groupCall.startedVoice": "{name} hat einen Sprachanruf gestartet",
+    "groupCall.startedVideo": "{name} hat einen Videoanruf gestartet",
+    "groupCall.inCall": "{count} im Anruf",
+    "groupCall.err.permission_denied": "Der Anruf konnte nicht starten - der Zugriff auf Mikrofon und Kamera ist blockiert. Erlaube ihn für diese Seite und versuche es erneut.",
+    "groupCall.err.device_not_found": "Der Anruf konnte nicht starten - auf diesem Gerät wurde kein Mikrofon gefunden.",
+    "groupCall.err.device_busy": "Der Anruf konnte nicht starten - dein Mikrofon wird von einer anderen App verwendet. Schließe sie und versuche es erneut.",
+    "groupCall.err.media_failed": "Der Anruf konnte nicht starten - das Mikrofon ließ sich nicht öffnen.",
+    "groupCall.err.call_in_progress": "In dieser Gruppe läuft bereits ein Anruf. Tritt ihm bei, statt einen neuen zu starten.",
+    "groupCall.err.not_ready": "Bestätige zuerst den Gruppencode, bevor du anrufst.",
+    "groupCall.speaking": "{name} spricht",
+    "groupCall.pin": "{name} groß anzeigen",
+    "groupCall.unpin": "Zurück zu allen",
+    "groupCall.showEveryone": "Alle"
   }
 }