Update version badges from v4.0 to v4.1

- Update all v4.0 badges to v4.1 across templates
- Add cute v4.1 badge under Stegasoo title in navbar

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/templates/decode.html

@@ -344,7 +344,7 @@
                           <div class="security-box h-100">
                             <label class="form-label">
                                 <i class="bi bi-broadcast me-1"></i> Channel
-                                <span class="badge bg-info ms-1">v4.0</span>
+                                <span class="badge bg-info ms-1">v4.1</span>
                                 <a href="/about#channel-keys" class="text-muted ms-1" title="Learn about channels"><i class="bi bi-info-circle"></i></a>
                             </label>