Service: isolate the profile in ProgramData, out of all normal profile paths

Local checkpoint - NOT for public release. Ed: the service profile must never be
reachable except through the Service menu.

Also fixes a real bug: the service runs as SYSTEM, whose per-user data folder is NOT the
interactive user's - so a profile saved in the user's profiles folder (or AppConfig, both
per-user) was invisible to the service. It would have idled, never streaming.

- New RemSound.Core.ServiceStore: the service profile + its settings (logging) live in a
  MACHINE-WIDE ProgramData\RemSound\service location - same absolute path for the user
  (config dialog) and SYSTEM (service). Moved ServiceProfileName/ServiceLoggingEnabled off
  AppConfig (per-user) onto this store.
- ServiceSendHost.FromConfig + RemSoundService now read ServiceStore; ConfigureServiceProfile
  saves there (and migrates + deletes any profile left in the old user-folder location).
- Because it's no longer in the user's profiles folder, it can't appear in the startup
  picker, File->Open, Recent profiles, or the password manager (all of which read the user
  ProfileStore); the reserved-title filter in ListProfileTitles stays as belt-and-braces.
- Password button renamed "Set service profile password".
- New self-test "Service profile isolation": store is under ProgramData, the reserved title
  is filtered from the listing, and it round-trips through the machine-wide store.

Gate 27/27.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/RemSoundService.cs

@@ -50,7 +50,7 @@ public sealed class RemSoundService : ServiceBase
 
     private static bool SafeServiceLogging()
     {
-        try { return AppConfig.Load().ServiceLoggingEnabled; }
+        try { return ServiceStore.LoadLoggingEnabled(); }
         catch { return false; }
     }