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.CentralUI/Auth/SiteScopeService.cs

@@ -38,6 +38,7 @@ public sealed class SiteScopeService
     /// True when the user is not restricted to a site subset (no <c>SiteId</c>
     /// claims). System-wide users see and act on every site.
     /// </summary>
+    /// <returns>A task that resolves to <c>true</c> if the user has no site-scope restriction.</returns>
     public async Task<bool> IsSystemWideAsync()
         => (await ResolveAsync()).IsSystemWide;
 
@@ -46,6 +47,7 @@ public sealed class SiteScopeService
     /// system-wide user (callers should consult <see cref="IsSystemWideAsync"/>
     /// or use the filter/allowed helpers, which already account for that).
     /// </summary>
+    /// <returns>A task that resolves to the set of permitted site IDs (empty for system-wide users).</returns>
     public async Task<IReadOnlySet<int>> PermittedSiteIdsAsync()
         => (await ResolveAsync()).Sites;
 
@@ -54,6 +56,7 @@ public sealed class SiteScopeService
     /// see. A system-wide user gets the full list back unchanged.
     /// </summary>
     /// <param name="sites">The full set of sites to filter.</param>
+    /// <returns>A task that resolves to the filtered list of sites the user is permitted to see.</returns>
     public async Task<List<Site>> FilterSitesAsync(IEnumerable<Site> sites)
     {
         var (isSystemWide, allowed) = await ResolveAsync();
@@ -67,6 +70,7 @@ public sealed class SiteScopeService
     /// Must be re-checked server-side before any mutating cross-site command.
     /// </summary>
     /// <param name="siteId">The <c>Site.Id</c> to check.</param>
+    /// <returns>A task that resolves to <c>true</c> when the user may operate on the given site.</returns>
     public async Task<bool> IsSiteAllowedAsync(int siteId)
     {
         var (isSystemWide, allowed) = await ResolveAsync();