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>

frontend/src/lib/stores.ts

@@ -339,9 +339,8 @@ export async function saveProfile(name: string) {
 export function loadProfile(name: string) {
   patchbay.update(pb => ({ ...pb, active_profile: name }));
   const pb = get_store_value(patchbay);
-  if (pb.activated) {
-    applyPatchbay(pb);
-  }
+  // Always apply connections when explicitly loading a profile
+  applyPatchbay(pb);
   savePatchbayState();
 }