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">

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Modbus/ModbusAddressPreview.razor

@@ -0,0 +1,85 @@
+@page "/modbus/address-preview"
+@using ZB.MOM.WW.OtOpcUa.Driver.Modbus
+
+@*
+    #149 — standalone preview / sanity-check tool for Modbus address strings. The Admin UI
+    doesn't yet have a per-tag CRUD surface (tags are seeded via SQL or arrive at runtime
+    through ITagDiscovery), so the ModbusAddressEditor component shipped in #145 needs a
+    page where operators can paste an address string and confirm it parses to what they
+    expect before committing it to a config row.
+
+    Doubles as a "did the parser ship correctly" smoke target for QA + a copy-pasteable
+    grammar reference for users skimming the docs.
+*@
+
+<PageTitle>Modbus address preview</PageTitle>
+
+<div class="container py-4">
+    <h1>Modbus address preview</h1>
+    <p class="text-muted">
+        Paste an address string and watch the parser break it down field by field. Useful for
+        sanity-checking a tag spreadsheet row before adding it to a driver's <code>DriverConfig</code>.
+        Full grammar: <a href="https://github.com/" target="_blank">docs/v2/modbus-addressing.md</a>.
+    </p>
+
+    <div class="row g-3">
+        <div class="col-md-4">
+            <label class="form-label">PLC family hint (drives the family-native branch)</label>
+            <select class="form-select" @bind="_family">
+                @foreach (var f in Enum.GetValues<ModbusFamily>())
+                {
+                    <option value="@f">@f</option>
+                }
+            </select>
+        </div>
+        @if (_family == ModbusFamily.MELSEC)
+        {
+            <div class="col-md-4">
+                <label class="form-label">MELSEC sub-family</label>
+                <select class="form-select" @bind="_melsecSubFamily">
+                    @foreach (var f in Enum.GetValues<MelsecFamily>())
+                    {
+                        <option value="@f">@f</option>
+                    }
+                </select>
+            </div>
+        }
+    </div>
+
+    <div class="mt-4">
+        <ModbusAddressEditor @bind-AddressString="_address"
+                             Family="_family"
+                             MelsecSubFamily="_melsecSubFamily"/>
+    </div>
+
+    <h3 class="mt-5">Quick-reference grammar</h3>
+    <pre class="bg-light p-3 rounded small">@_grammarReference</pre>
+</div>
+
+@code {
+    private string? _address;
+    private ModbusFamily _family = ModbusFamily.Generic;
+    private MelsecFamily _melsecSubFamily = MelsecFamily.Q_L_iQR;
+
+    // Held as a const string rather than inline markup so the Razor parser doesn't try to
+    // interpret the angle-bracket grammar tokens as element open/close.
+    private const string _grammarReference = @"<region><offset>[.<bit>][:<type>[<len>]][:<order>][:<count>]
+
+Examples (post-#146 type codes):
+  40001                    HoldingRegisters[0], Int16
+  400001                   same, 6-digit form
+  40001:F                  Float32 (HR[0..1])
+  40001:F:CDAB             Float32 word-swapped
+  40001:STR20              20-char ASCII string
+  40001:S:5                Int16[5] array (3-field shorthand)
+  40001:I:CDAB:10          Int32[10] word-swapped (4-field strict)
+  40001.5                  bit 5 of HR[0]
+  HR1:I                    Int32 via mnemonic region (matches Wonderware)
+  C100                     Coil 100 (mnemonic, 1-based)
+  V2000:F:CDAB             DL205 V-memory at PDU 1024 (Family=DL205)
+  D100:I                   MELSEC D-register 100, Int32 (Family=MELSEC)
+
+Type codes: BOOL, S (Int16), US (UInt16), I (Int32), UI (UInt32),
+            I_64 (Int64), UI_64 (UInt64), F, D, BCD, BCD_32, STR<n>
+Byte order: ABCD (BE default), CDAB (word-swap), BADC (byte-swap), DCBA (full reverse)";
+}