mbproxy: remediate the 2026-05-16 code-review findings

Fixes every finding from the codereviews/2026-05-16 multi-agent review
(2 Critical, 20 Major, 38 Minor) and adds that review to the repo.

Highlights: dashboard XSS escape; response cache invalidated on the
write request (not just the response); ReloadValidator now runs at
startup so port collisions / duplicate names / malformed Resilience
profiles fail fast; AdminPort 0 genuinely disables the admin endpoint;
PlcListener accept-loop faults propagate to the supervisor's faulted
path; reconciler Restart builds before removing; Resilience pipelines
are restart-only from a frozen snapshot; multiplexer connect-race leak,
watchdog party-list snapshot, backend-response and FC16 framing
validation; frontend reconnect retry and util.js load guard; plus the
log-event/doc drift sweep and test-port hygiene.

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

mbproxy/tests/Mbproxy.Tests/Admin/StatusBroadcasterTests.cs

@@ -183,9 +183,10 @@ public sealed class StatusBroadcasterTests
         h.Sink.FleetPushes.Count.ShouldBeGreaterThanOrEqualTo(3,
             "the background loop must push the fleet snapshot every interval");
 
+        // StopAsync awaits the loop task before returning, so the loop is guaranteed
+        // terminated here — no settling delay is needed for the assertion to be sound.
         await h.Broadcaster.StopAsync();
         int afterStop = h.Sink.FleetPushes.Count;
-        await Task.Delay(400, TestContext.Current.CancellationToken);
         h.Sink.FleetPushes.Count.ShouldBe(afterStop, "no pushes may occur after StopAsync");
     }
 }