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/Proxy/ProxyWorker.cs

@@ -47,6 +47,10 @@ internal sealed partial class ProxyWorker : BackgroundService
     private readonly IServiceProvider _services;
     private AdminEndpointHost? _admin;
 
+    // Per-PLC tag-value captures for the connection-detail debug view. Populated as
+    // each PerPlcContext is built; the admin SignalR layer arms/disarms entries.
+    private readonly TagCaptureRegistry _captureRegistry;
+
     // Supervisors are managed jointly by ProxyWorker (initial bootstrap) and
     // ConfigReconciler (subsequent hot-reload changes). The dictionary is shared via
     // ConfigReconciler.Attach() after initial startup.
@@ -71,14 +75,16 @@ internal sealed partial class ProxyWorker : BackgroundService
         ILogger<ProxyWorker> logger,
         ILoggerFactory loggerFactory,
         ConfigReconciler reconciler,
+        TagCaptureRegistry captureRegistry,
         IServiceProvider services)
     {
-        _options       = options;
-        _pipeline      = pipeline;
-        _logger        = logger;
-        _loggerFactory = loggerFactory;
-        _reconciler    = reconciler;
-        _services      = services;
+        _options         = options;
+        _pipeline        = pipeline;
+        _logger          = logger;
+        _loggerFactory   = loggerFactory;
+        _reconciler      = reconciler;
+        _captureRegistry = captureRegistry;
+        _services        = services;
         // Admin endpoint resolved lazily in ExecuteAsync (see field comment).
     }
 
@@ -123,6 +129,7 @@ internal sealed partial class ProxyWorker : BackgroundService
                 Counters = new ProxyCounters(),
                 Logger   = _loggerFactory.CreateLogger($"Mbproxy.Proxy.BcdRewriter.{plc.Name}"),
                 Cache    = cache,
+                Capture  = _captureRegistry.GetOrCreate(plc.Name, result.Map),
             };
         }