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

src/i18n/index.js

@@ -148,6 +148,29 @@ export function direction(code = currentLocale()) {
  */
 export const LTR_TEXT = { dir: 'ltr', style: { unicodeBidi: 'isolate', textAlign: 'start' } };
 
+/**
+ * The suggestion is an offer, and an offer that keeps coming back after it was turned
+ * down is an ad. One dismissal is remembered for good; storage can be unavailable, in
+ * which case the bar simply comes back — a worse experience, never a broken one.
+ */
+const SUGGEST_KEY = 'securebit-locale-suggest-dismissed';
+
+export function localeSuggestionDismissed() {
+    try {
+        return localStorage.getItem(SUGGEST_KEY) === '1';
+    } catch (_) {
+        return false;
+    }
+}
+
+export function dismissLocaleSuggestion() {
+    try {
+        localStorage.setItem(SUGGEST_KEY, '1');
+    } catch (_) {
+        // Nothing to do: the bar reappears next visit, which is not worth an exception.
+    }
+}
+
 /**
  * A locale the visitor would probably rather read, when it is not the one they are on.
  * Used to offer a link, never to redirect: an automatic redirect sends Googlebot —