Bump to v3.0.1: move UPnP discovery off the UI thread (fixes hang on Andre's network)

Bug: ticking the "Automatically open my router for incoming connections
(UPnP)" box in Preferences could freeze the WinForms message pump until
Mono.Nat's NatUtility.StartDiscovery() returned. On Andre's setup it never
did — audio kept flowing (audio threads are independent of the UI thread)
but the window stopped repainting, the system-tray hotkey stopped
responding, and the only way out was Task Manager.

Pre-existing latent bug in the v2.1 UPnP code; we just shipped without
anyone exercising the path on a problematic network (multiple adapters /
VPN / SSDP-swallowing router).

Fix: three call sites moved off the UI thread via Task.Run -
  * MainForm OnShown (startup re-enable from saved AppConfig.UpnpEnabled)
  * MainForm Preferences applyUpnpEnabled callback (user ticks the box)
  * MainForm power-resume handler (Refresh() after sleep/wake)
RouterPortMapper.Start() returns "immediately" only when StartDiscovery
returns quickly; on a slow network it can block synchronously for many
seconds. Same is true of Stop()'s socket teardown and Refresh()'s
teardown-then-restart sequence. All three are now safely backgrounded.

StatusChanged is unaffected - it already fires on the mapper's own thread
and the PreferencesDialog handler BeginInvokes back to the UI thread.
Live status label updates correctly during the new background discovery.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/RemSound.App/RemSound.App.csproj

@@ -14,7 +14,7 @@
          tag_name on the latest GitHub release; bump it on every public release. The
          AssemblyVersion / FileVersion default to this value, and Assembly.GetName().Version
          is what the About dialog and the updater both read. -->
-    <Version>3.0.0</Version>
+    <Version>3.0.1</Version>
   </PropertyGroup>
 
   <ItemGroup>