docs: add XML doc comments across src + Sister Projects section in CLAUDE.md

Bulk CommentChecker pass: fills in <param>/<inheritdoc> tags on public
APIs across all 23 src/ projects so the doc-coverage gate is green. Also
adds a Sister Projects section to CLAUDE.md pointing at the MxAccess
Gateway and OtOpcUa sibling repos, and gitignores local credential
captures (*login*.txt) and the wonder-app-vd03 deploy/ artifacts.

src/ScadaLink.AuditLog/Site/FallbackAuditWriter.cs

@@ -44,6 +44,11 @@ public sealed class FallbackAuditWriter : IAuditWriter
     /// <see cref="ServiceCollectionExtensions.AddAuditLog"/> registration
     /// always passes the real filter through.
     /// </summary>
+    /// <param name="primary">The primary audit writer (typically the SQLite writer).</param>
+    /// <param name="ring">Drop-oldest ring buffer used to stash events when the primary fails.</param>
+    /// <param name="failureCounter">Counter incremented on each primary failure for health reporting.</param>
+    /// <param name="logger">Logger for diagnostics.</param>
+    /// <param name="filter">Optional payload filter applied before writing; null means no filtering.</param>
     public FallbackAuditWriter(
         IAuditWriter primary,
         RingBufferFallback ring,
@@ -58,6 +63,7 @@ public sealed class FallbackAuditWriter : IAuditWriter
         _filter = filter; // null = no-op pass-through; see WriteAsync.
     }
 
+    /// <inheritdoc />
     public async Task WriteAsync(AuditEvent evt, CancellationToken ct = default)
     {
         ArgumentNullException.ThrowIfNull(evt);