fix(twincat): review fixes for sum-read and diagnostics (#645)

Strict width+kind eligibility for sum-batched scalars (others read singly); latch only on ADS
1793/1794, split 1792/1797/1798 without latching; 32 KiB per-command budget and 500-item ceiling;
short sum response handled per item. Diagnostics: opt-in diagnosticsEnabled (default off), reuse the
probe's ReadState, sample after the host-state transition, JitterMs renamed HeadroomMs, compact
per-device line so many devices fit the 16-entry cap, unavailable-symbol latch cleared on reconnect.
AdminUI: min/max on sum-read max, diagnostics checkbox. Pure planner extracted and unit-tested.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/TwinCATDriverPageFormSerializationTests.cs

@@ -74,6 +74,7 @@ public sealed class TwinCATDriverPageFormSerializationTests
             NotificationMaxDelayMs = 100,
             UseSumRead = true,
             SumReadMaxItems = 64,
+            DiagnosticsEnabled = true,
             Probe = new TwinCATProbeOptions
             {
                 Enabled = true,
@@ -92,6 +93,7 @@ public sealed class TwinCATDriverPageFormSerializationTests
         roundTripped.NotificationMaxDelayMs.ShouldBe(100);
         roundTripped.UseSumRead.ShouldBeTrue();
         roundTripped.SumReadMaxItems.ShouldBe(64);
+        roundTripped.DiagnosticsEnabled.ShouldBeTrue();
         roundTripped.Probe.Enabled.ShouldBeTrue();
         roundTripped.Probe.Interval.ShouldBe(TimeSpan.FromSeconds(6));
         roundTripped.Probe.Timeout.ShouldBe(TimeSpan.FromSeconds(2));