mbproxy: replace status page with a live SignalR web dashboard

The single auto-refreshing zero-JS status page gave operators a 25-column
wall and no way to drill into one connection. This adds a Bootstrap fleet
dashboard (filterable/sortable KPI table) and a per-PLC detail page with a
real-time debug view of raw PLC-side BCD vs. decoded client-side values,
streamed live over a SignalR feed. The debug view is fed by an on-demand
per-tag value capture, armed only while a detail page is open. All assets
(Bootstrap, SignalR client, fonts) are embedded so the UI works unchanged
on firewalled networks; GET /status.json is untouched for scrapers.

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

mbproxy/tests/Mbproxy.Tests/Configuration/ReloadValidatorTests.cs

@@ -334,4 +334,36 @@ public sealed class ReloadValidatorTests
         Assert.False(valid);
         Assert.Contains(errors, e => e.Contains("BackendHeartbeatIdleMs"));
     }
+
+    // ── AdminPushIntervalMs ────────────────────────────────────────────────────
+
+    [Fact]
+    public void Validate_AdminPushIntervalMs_Zero_Fails()
+    {
+        var opts = new MbproxyOptions
+        {
+            Plcs                = [MakePlc("PLC-A", 5020)],
+            AdminPushIntervalMs = 0,
+        };
+
+        bool valid = ReloadValidator.Validate(opts, out var errors);
+
+        Assert.False(valid);
+        Assert.Contains(errors, e => e.Contains("AdminPushIntervalMs"));
+    }
+
+    [Fact]
+    public void Validate_AdminPushIntervalMs_Negative_Fails()
+    {
+        var opts = new MbproxyOptions
+        {
+            Plcs                = [MakePlc("PLC-A", 5020)],
+            AdminPushIntervalMs = -5,
+        };
+
+        bool valid = ReloadValidator.Validate(opts, out var errors);
+
+        Assert.False(valid);
+        Assert.Contains(errors, e => e.Contains("AdminPushIntervalMs"));
+    }
 }