Harden OOBE, launch-source and elevation flow

Introduce a per-user OOBE state model and hardened launch/elevation handling. Adds OobeStateFile/OobeLaunchDecision models, OobeStateService (persisting %LOCALAPPDATA%/.launcher/state/oobe-state.json), and LauncherExecutionContext to capture elevation and user SID. CommandContext now normalizes/infers launch-source values (normal, postinstall, apply-update, plugin-install, debug-preview) and exposes maintenance checks. LauncherFlowCoordinator propagates richer launcher context details for diagnostics and suppresses OOBE for elevated/maintenance contexts. PluginInstallerService avoids requesting elevation for user-scoped installs and returns a clear error when installation target is outside the current user's LocalAppData. LauncherClient maps and surfaces result codes, UpdateWorkflow and installer invocation now pass explicit --launch-source values, and WelcomeOobeStep persists OOBE completion via the new service. Adds unit tests (CommandContext, OobeStateService, PluginInstallerService), docs/specs/checklists for the contract, and makes internals visible to tests.

LanMountainDesktop.Launcher/Services/LegacyVersionDetector.cs

@@ -262,6 +262,9 @@ internal sealed class LegacyVersionDetector
                 var parts = info.UninstallCommand.Split(new[] { ' ' }, 2);
                 var fileName = parts[0].Trim('"');
                 var arguments = parts.Length > 1 ? parts[1] : "";
+                Logger.Info(
+                    $"Opening legacy uninstall interface with elevation reason 'legacy_uninstall'. " +
+                    $"InstallPath='{info.InstallPath}'; Version='{info.Version}'.");
 
                 Process.Start(new ProcessStartInfo
                 {