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/Models/OobeStateModels.cs

@@ -0,0 +1,63 @@
+namespace LanMountainDesktop.Launcher.Models;
+
+internal enum OobeStateStatus
+{
+    FirstRun,
+    Completed,
+    Unavailable,
+    Suppressed
+}
+
+internal sealed class OobeStateFile
+{
+    public int SchemaVersion { get; init; } = 1;
+
+    public string CompletedAtUtc { get; init; } = string.Empty;
+
+    public string UserName { get; init; } = string.Empty;
+
+    public string? UserSid { get; init; }
+
+    public string LaunchSource { get; init; } = string.Empty;
+}
+
+internal sealed class OobeLaunchDecision
+{
+    public OobeStateStatus Status { get; init; }
+
+    public bool ShouldShowOobe { get; init; }
+
+    public string StatePath { get; init; } = string.Empty;
+
+    public string LaunchSource { get; init; } = "normal";
+
+    public bool IsElevated { get; init; }
+
+    public string UserName { get; init; } = string.Empty;
+
+    public string? UserSid { get; init; }
+
+    public string ResultCode { get; init; } = "ok";
+
+    public string SuppressionReason { get; init; } = string.Empty;
+
+    public string ErrorMessage { get; init; } = string.Empty;
+
+    public bool UsedLegacyMarker { get; init; }
+
+    public bool MigratedLegacyMarker { get; init; }
+}
+
+internal sealed class OobeCompletionResult
+{
+    public bool Success { get; init; }
+
+    public string ResultCode { get; init; } = "ok";
+
+    public string ErrorMessage { get; init; } = string.Empty;
+}
+
+internal sealed record LauncherExecutionSnapshot(
+    bool IsElevated,
+    string UserName,
+    string? UserSid);