docs: complete XML doc coverage (returns, summaries, inheritdoc)

Resolve all 622 issues flagged by the enhanced CommentChecker: add missing
<returns> tags (incl. the standard phrasing on non-generic Task methods),
add missing <summary> tags, and replace misused/redundant <inheritdoc/> on
members that override or implement nothing with real documentation.
Documentation-only — no behavior change; solution builds clean.

src/ZB.MOM.WW.ScadaBridge.StoreAndForward/StoreAndForwardService.cs

@@ -210,6 +210,7 @@ public class StoreAndForwardService
     /// <summary>
     /// Initializes storage and starts the background retry timer.
     /// </summary>
+    /// <returns>A task representing the asynchronous start operation.</returns>
     public async Task StartAsync()
     {
         await _storage.InitializeAsync();
@@ -265,6 +266,7 @@ public class StoreAndForwardService
     /// (with a bounded <see cref="SweepShutdownWaitTimeout"/> so a hung
     /// dependency cannot block host shutdown indefinitely) before returning.
     /// </summary>
+    /// <returns>A task representing the asynchronous stop operation.</returns>
     public async Task StopAsync()
     {
         if (_retryTimer != null)
@@ -371,6 +373,7 @@ public class StoreAndForwardService
     /// non-routed run and for callers (notifications, pre-Task-6 callers) that
     /// do not supply one.
     /// </param>
+    /// <returns>A task that resolves to a result indicating whether the message was delivered or buffered.</returns>
     public async Task<StoreAndForwardResult> EnqueueAsync(
         StoreAndForwardCategory category,
         string target,
@@ -469,6 +472,7 @@ public class StoreAndForwardService
     /// <summary>
     /// WP-10: Background retry sweep. Processes all pending messages that are due for retry.
     /// </summary>
+    /// <returns>A task representing the asynchronous retry sweep.</returns>
     internal async Task RetryPendingMessagesAsync()
     {
         // Prevent overlapping retry sweeps