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/hi.json

@@ -31,6 +31,9 @@
   },
   "ui": {
     "language.label": "भाषा",
+    "language.suggest.text": "यह पृष्ठ हिन्दी में भी उपलब्ध है।",
+    "language.suggest.cta": "हिन्दी में पढ़ें",
+    "language.suggest.dismiss": "बंद करें",
     "community.title": "निजता के भविष्य में शामिल हों",
     "community.description": "SecureBit अपने समुदाय से बढ़ता है। आपके विचार और सुझाव सुरक्षित संवाद का भविष्य गढ़ते हैं - खुले में बना, और पूरे रास्ते पूरी ASN.1 जाँच के साथ।",
     "community.github": "GitHub रिपॉज़िटरी",
@@ -776,7 +779,29 @@
     "offline.disconnect": "जुड़ाव तोड़ें",
     "offline.learnMore": "और जानें",
     "pwa.installApp": "ऐप इंस्टॉल करें",
-    "chat.onWeb": "आप वेब संस्करण पर हैं"
+    "chat.onWeb": "आप वेब संस्करण पर हैं",
+    "groupCall.startVoice": "समूह वॉइस कॉल शुरू करें",
+    "groupCall.startVideo": "समूह वीडियो कॉल शुरू करें",
+    "groupCall.join": "शामिल हों",
+    "groupCall.dismiss": "अभी नहीं",
+    "groupCall.leave": "कॉल छोड़ें",
+    "groupCall.you": "आप",
+    "groupCall.connecting": "जुड़ रहा है…",
+    "groupCall.waitingLink": "सीधे लिंक की प्रतीक्षा…",
+    "groupCall.legFailed": "कनेक्ट नहीं हो सका",
+    "groupCall.startedVoice": "{name} ने वॉइस कॉल शुरू की",
+    "groupCall.startedVideo": "{name} ने वीडियो कॉल शुरू की",
+    "groupCall.inCall": "कॉल में {count}",
+    "groupCall.err.permission_denied": "कॉल शुरू नहीं हो सकी - माइक्रोफ़ोन और कैमरे की अनुमति अवरुद्ध है। इस साइट के लिए अनुमति दें और फिर कोशिश करें।",
+    "groupCall.err.device_not_found": "कॉल शुरू नहीं हो सकी - इस डिवाइस पर कोई माइक्रोफ़ोन नहीं मिला।",
+    "groupCall.err.device_busy": "कॉल शुरू नहीं हो सकी - आपका माइक्रोफ़ोन किसी अन्य ऐप के उपयोग में है। उसे बंद करके फिर कोशिश करें।",
+    "groupCall.err.media_failed": "कॉल शुरू नहीं हो सकी - माइक्रोफ़ोन नहीं खुल सका।",
+    "groupCall.err.call_in_progress": "इस समूह में पहले से एक कॉल चल रही है। नई शुरू करने के बजाय उसमें शामिल हों।",
+    "groupCall.err.not_ready": "कॉल करने से पहले समूह कोड की पुष्टि करें।",
+    "groupCall.speaking": "{name} बोल रहे हैं",
+    "groupCall.pin": "{name} को बड़ा दिखाएँ",
+    "groupCall.unpin": "सभी पर लौटें",
+    "groupCall.showEveryone": "सभी"
   },
   "manifest": {
     "name": "SecureBit.chat - निजी, एन्क्रिप्टेड मैसेंजर",