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.ManagementService/DebugStreamHub.cs

@@ -33,6 +33,7 @@ public class DebugStreamHub : Hub
     /// <param name="roles">Roles held by the connected user.</param>
     /// <param name="permittedSiteIds">Site ids the user is scoped to; empty means system-wide.</param>
     /// <param name="instanceSiteId">Site id of the instance being subscribed to.</param>
+    /// <returns><see langword="true"/> if the user may subscribe to the instance; otherwise <see langword="false"/>.</returns>
     public static bool IsInstanceAccessAllowed(
         IReadOnlyCollection<string> roles,
         IReadOnlyCollection<string> permittedSiteIds,
@@ -134,6 +135,7 @@ public class DebugStreamHub : Hub
     /// Sends the initial snapshot immediately, then streams incremental changes.
     /// </summary>
     /// <param name="instanceId">Database id of the instance to subscribe to.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task SubscribeInstance(int instanceId)
     {
         // Stop any existing subscription for this connection
@@ -222,6 +224,7 @@ public class DebugStreamHub : Hub
     /// <summary>
     /// Unsubscribes from the current debug stream.
     /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     public Task UnsubscribeInstance()
     {
         if (Context.Items.TryGetValue(SessionIdKey, out var sessionIdObj) && sessionIdObj is string sessionId)