chore(release): renumber group calls as v6.7.0

Group calls are a new capability, and 6.6.6 only landed as a patch because the
version was bumped once per deploy while the feature was being tested. The
number is the release's, not the deploy's.

No code changes: version, badge, changelog heading, docs and build stamp.

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

dist/app-boot.js

@@ -31684,7 +31684,7 @@ var SecureMasterKeyManager = class {
 var import_NotificationIntegration = __toESM(require_NotificationIntegration());
 
 // package.json
-var version = "6.6.6";
+var version = "6.7.0";
 
 // src/components/ui/LanguageSwitcher.jsx
 var LanguageSwitcher = () => {