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.SiteEventLogging/EventLogPurgeService.cs

@@ -17,6 +17,7 @@ namespace ZB.MOM.WW.ScadaBridge.SiteEventLogging;
 /// active" so non-clustered hosts and unit tests are unaffected — backward
 /// compatible with the prior "run on every host" behaviour.
 /// </summary>
+/// <returns><c>true</c> if this node is the active site member and should run the purge; <c>false</c> to skip.</returns>
 public delegate bool SiteEventLogActiveNodeCheck();
 
 /// <summary>
@@ -200,6 +201,7 @@ public class EventLogPurgeService : BackgroundService
     /// the raw file size from <c>page_count</c>) means the storage-cap loop observes
     /// space being reclaimed even if free pages have not yet been returned to the OS.
     /// </summary>
+    /// <returns>The logical database size in bytes (used pages × page size).</returns>
     internal long GetDatabaseSizeBytes()
     {
         return _eventLogger.WithConnection(connection =>

src/ZB.MOM.WW.ScadaBridge.SiteEventLogging/IEventLogQueryService.cs

@@ -12,5 +12,6 @@ public interface IEventLogQueryService
     /// Executes a query against the local site event log and returns the matching entries.
     /// </summary>
     /// <param name="request">The query parameters including filters, pagination, and keyword search.</param>
+    /// <returns>The query response containing the matching log entries and pagination metadata.</returns>
     EventLogQueryResponse ExecuteQuery(EventLogQueryRequest request);
 }

src/ZB.MOM.WW.ScadaBridge.SiteEventLogging/ISiteEventLogger.cs

@@ -20,6 +20,7 @@ public interface ISiteEventLogger
     /// Optional free-form detail text (stack traces, compilation errors, etc.).
     /// Stored verbatim — JSON is conventional but not validated or enforced.
     /// </param>
+    /// <returns>A task that completes once the event is durably persisted.</returns>
     Task LogEventAsync(
         string eventType,
         string severity,

src/ZB.MOM.WW.ScadaBridge.SiteEventLogging/ServiceCollectionExtensions.cs

@@ -11,6 +11,7 @@ public static class ServiceCollectionExtensions
     /// Register site event logging services (recording, purge, query).
     /// </summary>
     /// <param name="services">The DI service collection to register into.</param>
+    /// <returns>The same <see cref="IServiceCollection"/> for chaining.</returns>
     public static IServiceCollection AddSiteEventLogging(this IServiceCollection services)
     {
         // The recorder is registered as a concrete singleton and the interface is

src/ZB.MOM.WW.ScadaBridge.SiteEventLogging/SiteEventLogger.cs

@@ -89,17 +89,7 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
         _writerLoop = Task.Run(ProcessWriteQueueAsync);
     }
 
-    /// <summary>
-    /// SiteEventLogging-018: number of event writes that have failed (SQLite
-    /// error, disk full, bounded-queue overflow drop, etc.) since this logger
-    /// was created. Available for future Health Monitoring integration — the
-    /// counter is correct and observable, but the central health-metric
-    /// pipeline does not yet poll it, so a sustained non-zero value currently
-    /// goes unnoticed in production beyond the per-failure log line. Wiring
-    /// the metric into the 30-second site-metric publish is tracked
-    /// separately; promoted to <see cref="ISiteEventLogger"/> so the eventual
-    /// consumer reads it without a concrete-type downcast.
-    /// </summary>
+    /// <inheritdoc />
     public long FailedWriteCount => Interlocked.Read(ref _failedWriteCount);
 
     /// <summary>
@@ -110,6 +100,7 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
     /// been disposed.
     /// </summary>
     /// <param name="action">The action to run against the shared connection.</param>
+    /// <returns><see langword="true"/> if the action was executed; <see langword="false"/> if the logger is disposed.</returns>
     internal bool WithConnection(Action<SqliteConnection> action)
     {
         ArgumentNullException.ThrowIfNull(action);
@@ -128,6 +119,7 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
     /// </summary>
     /// <typeparam name="T">The return type of the function.</typeparam>
     /// <param name="func">The function to run against the shared connection.</param>
+    /// <returns>The value returned by <paramref name="func"/>.</returns>
     internal T WithConnection<T>(Func<SqliteConnection, T> func)
     {
         ArgumentNullException.ThrowIfNull(func);