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.NotificationService/CredentialRedactor.cs

@@ -33,6 +33,16 @@ public static class CredentialRedactor
     /// </summary>
     private const int MinSecretLength = 12;
 
+    /// <summary>
+    /// Returns <paramref name="text"/> with every secret component of the supplied
+    /// colon-delimited credential string masked.
+    /// </summary>
+    /// <param name="text">The text to scrub (e.g. an exception message). Returns empty string if null.</param>
+    /// <param name="credentials">
+    /// The credential string in use — Basic Auth <c>user:pass</c> or OAuth2
+    /// <c>tenantId:clientId:clientSecret</c>. May be null; returns <paramref name="text"/> unmodified when null.
+    /// </param>
+    /// <returns>The scrubbed text with secret components replaced by <c>***REDACTED***</c>.</returns>
     public static string Scrub(string? text, string? credentials)
     {
         if (string.IsNullOrEmpty(text) || string.IsNullOrEmpty(credentials))