fix: mute race condition + profile loading + add Update button

Bug 1 - Mute unmute not sticking (G560 and others):
- Root cause: on_node_info was reading volume/mute from info->props which
  contains static initial values only — NOT updated at runtime. When any
  node info event fired, it overwrote the correct runtime state with stale
  initial data, causing the unmute to revert on the next graph event.
- Fix: Subscribe nodes to SPA_PARAM_Props in addition to SPA_PARAM_Format.
  Handle SPA_PARAM_Props in on_node_param to track volume (both SPA_PROP_volume
  and SPA_PROP_channelVolumes averaged) and mute from the authoritative live
  parameter stream. Remove stale volume/mute reads from on_node_info.
- Also fix mute detection in /api/mute: check "mute":true precisely instead
  of searching for bare "true" anywhere in the body.

Bug 2 - Loading profiles does not work:
- loadProfile was only applying connections when already in "activated" mode.
  Load now always applies the profile connections immediately.

Bug 3 - No option to update an existing profile:
- Add "Update" button in profile list that overwrites the profile with current
  connections (calls saveProfile with the existing name).
- Clear the profile name input after "Save Current" succeeds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/web_server.cpp

@@ -442,7 +442,9 @@ void WebServer::setupRoutes() {
         if (sscanf(req.body.c_str(), "{\"node_id\":%u", &node_id) == 1 ||
             sscanf(req.body.c_str(), "{\"node_id\": %u", &node_id) == 1)
         {
-            bool mute = req.body.find("true") != std::string::npos;
+            // Check for "mute":true precisely — the old `find("true")` was imprecise
+            bool mute = req.body.find("\"mute\":true") != std::string::npos ||
+                        req.body.find("\"mute\": true") != std::string::npos;
             bool ok = m_engine.setNodeMute(node_id, mute);
             if (ok) broadcastGraph();
             res.set_content(ok ? "{\"ok\":true}" : "{\"ok\":false}", "application/json");