Replace GVFS.Service with machine-wide logon task and LocalRepoRegistry

Replace the GVFS.Service Windows service with a simpler architecture:

Infrastructure:
- LocalRepoRegistry: file-based repo tracking, wire-compatible with old
  service format. SYSTEM uses ProgramData; per-user uses platform default.
  Seed-on-first-use copies accessible entries from system registry.
- LogonTaskRegistration: machine-wide \GVFS\AutoMount task fires for all
  interactive users (GroupId S-1-5-4) at logon, runs gvfs service --mount-all.
  Each user's repos loaded from their own LocalRepoRegistry.
- ProjFS boot task: enable-projfs-on-all-drives.ps1 enables ProjFS and
  attaches PrjFlt on all volumes. Embedded in task XML via build-task-xml.ps1
  with SHA-256 hash marker for drift detection.
- CLI verb fallbacks: mount/unmount/service verbs fall back to LocalRepoRegistry
  when the service named pipe is unavailable.
- GVFSVerb: silent-success fallback for PrjFlt FilterAttach.
- InProcessMount: restore exception safety net in HandleRequest.

Installer:
- Stop and delete GVFS.Service on upgrade from older versions.
- Register \GVFS\AutoMount logon task.
- Remove service deployment, install, start from [Files]/[Run].
- Remove PendingUpgrade staging logic and ShowMountChoiceDialog.
- Exclude GVFS.Service.exe from payload (layout.bat).

Functional tests:
- Remove service install/uninstall (no service to test against).
- Settings.cs auto-detects user-mode gvfs at %LocalAppData%\VFSForGit\Current.

926 unit tests pass.

Assisted-by: Claude Sonnet 4.5
Assisted-by: Claude Opus 4.6
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: tyrielv

GVFS/GVFS.Common/IScheduledTaskInvoker.cs

@@ -0,0 +1,37 @@
+using System.Collections.Generic;
+
+namespace GVFS.Common
+{
+    /// <summary>
+    /// Abstracts the Windows Task Scheduler operations needed by
+    /// <see cref="LogonTaskRegistration"/>. Production callers use
+    /// <see cref="SchTasksScheduledTaskInvoker"/>; tests pass a mock so
+    /// they can exercise <see cref="LogonTaskRegistration"/>'s logic
+    /// without actually touching the Task Scheduler on the test machine.
+    /// </summary>
+    public interface IScheduledTaskInvoker
+    {
+        /// <summary>
+        /// Register the task at <paramref name="taskPath"/> from the given
+        /// XML, overwriting any existing task at that path. Returns
+        /// <c>true</c> on success.
+        /// </summary>
+        bool TryRegisterFromXml(string taskPath, string xml, out string errorMessage);
+
+        /// <summary>
+        /// Read back the registered XML for the task at
+        /// <paramref name="taskPath"/>. Returns <c>true</c> with the XML
+        /// when the task exists; returns <c>false</c> with a populated
+        /// <paramref name="errorMessage"/> when it does not.
+        /// </summary>
+        bool TryQueryXml(string taskPath, out string xml, out string errorMessage);
+
+        /// <summary>
+        /// Unregister the task at <paramref name="taskPath"/>. Returns
+        /// <c>true</c> if the task was unregistered OR was not registered
+        /// to begin with (idempotent). Returns <c>false</c> only on a hard
+        /// failure (e.g., permission denied).
+        /// </summary>
+        bool TryUnregister(string taskPath, out string errorMessage);
+    }
+}

GVFS/GVFS.Common/LocalRepoRegistration.cs

@@ -0,0 +1,64 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace GVFS.Common
+{
+    /// <summary>
+    /// One entry in the user-level repo registry on disk. Field set and
+    /// JSON shape MUST match GVFS.Service.RepoRegistration so that the
+    /// user-level registry file (written by <see cref="LocalRepoRegistry"/>)
+    /// is wire-compatible with any registry the legacy service has written
+    /// in the past. If a new field is added here, the same field must also
+    /// be added to GVFS.Service.RepoRegistration (and vice versa) along
+    /// with a registry-format-version bump.
+    /// </summary>
+    public class LocalRepoRegistration
+    {
+        public LocalRepoRegistration()
+        {
+        }
+
+        public LocalRepoRegistration(string enlistmentRoot, string ownerSID)
+        {
+            this.EnlistmentRoot = enlistmentRoot;
+            this.OwnerSID = ownerSID;
+            this.IsActive = true;
+        }
+
+        public string EnlistmentRoot { get; set; }
+        public string OwnerSID { get; set; }
+        public bool IsActive { get; set; }
+
+        // Uses LocalRepoRegistrationJsonContext (assembly-local source generator)
+        // rather than GVFSJsonContext. The service-side RepoRegistration uses
+        // its own ServiceJsonContext for the same reason — neither type can be
+        // registered in GVFSJsonContext because GVFSJsonContext lives in
+        // GVFS.Common and the service-side type lives in GVFS.Service (wrong
+        // dependency direction). Keeping symmetric local contexts here means
+        // the on-disk JSON shape is governed by identical source-gen behavior
+        // on both sides.
+        public static LocalRepoRegistration FromJson(string json)
+        {
+            return JsonSerializer.Deserialize(json, LocalRepoRegistrationJsonContext.Default.LocalRepoRegistration);
+        }
+
+        public string ToJson()
+        {
+            return JsonSerializer.Serialize(this, LocalRepoRegistrationJsonContext.Default.LocalRepoRegistration);
+        }
+
+        public override string ToString()
+        {
+            return string.Format(
+                "({0} - {1}) {2}",
+                this.IsActive ? "Active" : "Inactive",
+                this.OwnerSID,
+                this.EnlistmentRoot);
+        }
+    }
+
+    [JsonSerializable(typeof(LocalRepoRegistration))]
+    internal partial class LocalRepoRegistrationJsonContext : JsonSerializerContext
+    {
+    }
+}