Task #149 — Modbus address-preview page + ImportEquipment help

The original task scope assumed a per-tag editor lived in EquipmentTab.razor
or a similar surface. Reading the codebase confirmed that's not the case:
tags are seeded via SQL (scripts/smoke/*) or arrive at runtime through
ITagDiscovery; the Admin UI has no per-tag CRUD page today. Equipment
import is for equipment metadata (Name / MachineCode / ZTag / SAPID /
Identification) — not tag rows.

Adjusted scope:

1. ModbusAddressPreview.razor — new standalone page at /modbus/address-preview.
   Hosts the ModbusAddressEditor component shipped in #145 + the family
   selector + a copy-pasteable grammar reference. Operators can sanity-check
   address-string syntax (40001:F:CDAB / HR1:I / V2000:F / D100:I etc.)
   without committing it to a config row first.

2. ImportEquipment.razor — appended a secondary alert banner clarifying
   that Modbus per-tag addressing isn't part of equipment import; points
   users at the Drivers tab + the new preview tool.

Builds clean against the existing Admin app. The actual per-tag CRUD UI is
still a separate piece of work — when it ships, it can drop in
ModbusAddressEditor directly. The preview page acts as the canonical
demonstration of how to use the component.

Razor caveat: the grammar reference uses literal `<...>` syntax tokens
that the Razor parser interprets as malformed elements when inlined in a
<pre> block. Held as a string field (_grammarReference) and rendered
through @ binding to sidestep the parser conflict.

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Clusters/ImportEquipment.razor

@@ -26,6 +26,15 @@
     reservation conflict exists.
 </div>
 
+<div class="alert alert-secondary small mb-3">
+    <strong>Per-tag addressing for Modbus drivers</strong> isn't part of equipment import —
+    tags are configured at the driver-instance level via the
+    <a href="/clusters/@ClusterId/draft/@GenerationId">Drivers tab</a>. Use the
+    <a href="/modbus/address-preview" target="_blank">address-preview tool</a> to sanity-check
+    grammar strings (<code>40001:F:CDAB</code>, <code>HR1:I</code>, <code>V2000</code> for
+    DL205 family, etc.) before pasting them into the driver config.
+</div>
+
 <div class="card mb-3">
     <div class="card-body">
         <div class="row g-3">