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/src/Mbproxy/Options/MbproxyOptions.cs

@@ -7,6 +7,14 @@ public sealed class MbproxyOptions
     public BcdTagListOptions BcdTags { get; init; } = new();
     public IReadOnlyList<PlcOptions> Plcs { get; init; } = [];
     public int AdminPort { get; init; } = 8080;
+
+    /// <summary>
+    /// Server-push cadence (milliseconds) for the admin dashboard's SignalR feed.
+    /// Every interval the admin endpoint builds a status snapshot and pushes it to
+    /// connected dashboard / detail-page clients. Must be &gt; 0. Defaults to 1000.
+    /// </summary>
+    public int AdminPushIntervalMs { get; init; } = 1000;
+
     public ConnectionOptions Connection { get; init; } = new();
     public ResilienceOptions Resilience { get; init; } = new();
 
@@ -106,6 +114,9 @@ public sealed class MbproxyOptionsValidator : IValidateOptions<MbproxyOptions>
             errors.Add(
                 $"Connection.GracefulShutdownTimeoutMs must be > 0; got {options.Connection.GracefulShutdownTimeoutMs}.");
 
+        if (options.AdminPushIntervalMs <= 0)
+            errors.Add($"AdminPushIntervalMs must be > 0; got {options.AdminPushIntervalMs}.");
+
         // Keepalive section ranges. Cross-field rules (heartbeat interval vs request
         // timeout) are enforced in ReloadValidator.
         var ka = options.Connection.Keepalive;