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.Commons/Interfaces/Repositories/ISiteCallAuditRepository.cs

@@ -39,6 +39,7 @@ public interface ISiteCallAuditRepository
     /// </summary>
     /// <param name="siteCall">The site call row to insert or monotonically update.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     Task UpsertAsync(SiteCall siteCall, CancellationToken ct = default);
 
     /// <summary>
@@ -46,6 +47,7 @@ public interface ISiteCallAuditRepository
     /// </summary>
     /// <param name="id">The tracked operation id to look up.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that resolves to the matching <see cref="SiteCall"/>, or <c>null</c> if no row exists.</returns>
     Task<SiteCall?> GetAsync(TrackedOperationId id, CancellationToken ct = default);
 
     /// <summary>
@@ -58,6 +60,7 @@ public interface ISiteCallAuditRepository
     /// <param name="filter">Filter criteria for the query.</param>
     /// <param name="paging">Keyset paging parameters.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that resolves to a page of <see cref="SiteCall"/> rows matching the filter, ordered by creation time descending.</returns>
     Task<IReadOnlyList<SiteCall>> QueryAsync(
         SiteCallQueryFilter filter,
         SiteCallPaging paging,
@@ -71,6 +74,7 @@ public interface ISiteCallAuditRepository
     /// </summary>
     /// <param name="olderThanUtc">UTC cutoff; terminal rows older than this are deleted.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that resolves to the number of rows deleted.</returns>
     Task<int> PurgeTerminalAsync(DateTime olderThanUtc, CancellationToken ct = default);
 
     /// <summary>
@@ -84,6 +88,7 @@ public interface ISiteCallAuditRepository
     /// <param name="stuckCutoff">UTC threshold for classifying a row as stuck.</param>
     /// <param name="intervalSince">UTC start of the delivered/failed interval window.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that resolves to a global <see cref="SiteCallKpiSnapshot"/> computed from the current table state.</returns>
     Task<SiteCallKpiSnapshot> ComputeKpisAsync(
         DateTime stuckCutoff,
         DateTime intervalSince,
@@ -97,6 +102,7 @@ public interface ISiteCallAuditRepository
     /// <param name="stuckCutoff">UTC threshold for classifying a row as stuck.</param>
     /// <param name="intervalSince">UTC start of the delivered/failed interval window.</param>
     /// <param name="ct">Cancellation token.</param>
+    /// <returns>A task that resolves to a per-site KPI list; sites with no rows are omitted.</returns>
     Task<IReadOnlyList<SiteCallSiteKpiSnapshot>> ComputePerSiteKpisAsync(
         DateTime stuckCutoff,
         DateTime intervalSince,