Merge origin/main with local pending work and update AGENTS.md references

- Resolve 14 conflicts from popping local stash on top of origin's
  eed1e88 + 8d3352f doc-comment additions (11 mechanical, plus
  version.rs, DashboardAuthenticatorTests.cs, DashboardGalaxyProjector.cs)
- Fix 4 test files that used AGENTS.md as the repo-root sentinel
  (now use CLAUDE.md, since AGENTS.md was removed in 4731ab5)
- Redirect 10 doc citations from AGENTS.md to the matching gateway.md
  sections (Value Model, Status Model, Security, STA Worker Thread
  Model, gRPC Layer rule, cancellation rule)

Verified: solution build clean, x86 worker build clean, 266/266
gateway tests passing, 121/121 worker tests passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/dotnet/MxGateway.Client/MxGatewayClientOptions.cs

@@ -47,6 +47,8 @@ public sealed class MxGatewayClientOptions
     /// </summary>
     public TimeSpan? StreamTimeout { get; init; }
 
+    public int MaxGrpcMessageBytes { get; init; } = 16 * 1024 * 1024;
+
     /// <summary>
     /// Gets the retry configuration for safe unary calls.
     /// </summary>
@@ -102,6 +104,13 @@ public sealed class MxGatewayClientOptions
                 "The stream timeout must be greater than zero when configured.");
         }
 
+        if (MaxGrpcMessageBytes <= 0)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(MaxGrpcMessageBytes),
+                "The maximum gRPC message size must be greater than zero.");
+        }
+
         if (UseTls && Endpoint.Scheme != Uri.UriSchemeHttps)
         {
             throw new ArgumentException(