Driver-instance bootstrap pipeline (#248) — DriverInstance rows materialise as live IDriver instances

Closes the gap surfaced by Phase 7 live smoke (#240): DriverInstance rows in
the central config DB had no path to materialise as live IDriver instances in
DriverHost, so virtual-tag scripts read BadNodeIdUnknown for every tag.

## DriverFactoryRegistry (Core.Hosting)
Process-singleton type-name → factory map. Each driver project's static
Register call pre-loads its factory at Program.cs startup; the bootstrapper
looks up by DriverInstance.DriverType + invokes with (DriverInstanceId,
DriverConfig JSON). Case-insensitive; duplicate-type registration throws.

## GalaxyProxyDriverFactoryExtensions.Register (Driver.Galaxy.Proxy)
Static helper — no Microsoft.Extensions.DependencyInjection dep, keeps the
driver project free of DI machinery. Parses DriverConfig JSON for PipeName +
SharedSecret + ConnectTimeoutMs. DriverInstanceId from the row wins over JSON
per the schema's UX_DriverInstance_Generation_LogicalId.

## DriverInstanceBootstrapper (Server)
After NodeBootstrap loads the published generation: queries DriverInstance
rows scoped to that generation, looks up the factory per row, constructs +
DriverHost.RegisterAsync (which calls InitializeAsync). Per plan decision
#12 (driver isolation), failure of one driver doesn't prevent others —
logs ERR + continues + returns the count actually registered. Unknown
DriverType (factory not registered) logs WRN + skips so a missing-assembly
deployment doesn't take down the whole server.

## Wired into OpcUaServerService.ExecuteAsync
After NodeBootstrap.LoadCurrentGenerationAsync, before
PopulateEquipmentContentAsync + Phase7Composer.PrepareAsync. The Phase 7
chain now sees a populated DriverHost so CachedTagUpstreamSource has an
upstream feed.

## Live evidence on the dev box
Re-ran the Phase 7 smoke from task #240. Pre-#248 vs post-#248:
  Equipment namespace snapshots loaded for 0/0 driver(s)  ← before
  Equipment namespace snapshots loaded for 1/1 driver(s)  ← after

Galaxy.Host pipe ACL denied our SID (env-config issue documented in
docs/ServiceHosting.md, NOT a code issue) — the bootstrapper logged it as
"failed to initialize, driver state will reflect Faulted" and continued past
the failure exactly per plan #12. The rest of the pipeline (Equipment walker
+ Phase 7 composer) ran to completion.

## Tests — 5 new DriverFactoryRegistryTests
Register + TryGet round-trip, case-insensitive lookup, duplicate-type throws,
null-arg guards, RegisteredTypes snapshot. Pure functions; no DI/DB needed.
The bootstrapper's DB-query path is exercised by the live smoke (#240) which
operators run before each release.

src/ZB.MOM.WW.OtOpcUa.Core/Hosting/DriverFactoryRegistry.cs

@@ -0,0 +1,64 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Hosting;
+
+/// <summary>
+///     Process-singleton registry of <see cref="IDriver"/> factories keyed by
+///     <c>DriverInstance.DriverType</c> string. Each driver project ships a DI
+///     extension (e.g. <c>services.AddGalaxyProxyDriverFactory()</c>) that registers
+///     its factory at startup; the bootstrapper looks up the factory by
+///     <c>DriverInstance.DriverType</c> + invokes it with the row's
+///     <c>DriverInstanceId</c> + <c>DriverConfig</c> JSON.
+/// </summary>
+/// <remarks>
+///     Closes the gap surfaced by task #240 live smoke — DriverInstance rows in
+///     the central config DB had no path to materialise as registered <see cref="IDriver"/>
+///     instances. The factory registry is the seam.
+/// </remarks>
+public sealed class DriverFactoryRegistry
+{
+    private readonly Dictionary<string, Func<string, string, IDriver>> _factories
+        = new(StringComparer.OrdinalIgnoreCase);
+    private readonly object _lock = new();
+
+    /// <summary>
+    ///     Register a factory for <paramref name="driverType"/>. Throws if a factory is
+    ///     already registered for that type — drivers are singletons by type-name in
+    ///     this process.
+    /// </summary>
+    /// <param name="driverType">Matches <c>DriverInstance.DriverType</c>.</param>
+    /// <param name="factory">
+    ///     Receives <c>(driverInstanceId, driverConfigJson)</c>; returns a new
+    ///     <see cref="IDriver"/>. Must NOT call <see cref="IDriver.InitializeAsync"/>
+    ///     itself — the bootstrapper calls it via <see cref="DriverHost.RegisterAsync"/>
+    ///     so the host's per-driver retry semantics apply uniformly.
+    /// </param>
+    public void Register(string driverType, Func<string, string, IDriver> factory)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverType);
+        ArgumentNullException.ThrowIfNull(factory);
+        lock (_lock)
+        {
+            if (_factories.ContainsKey(driverType))
+                throw new InvalidOperationException(
+                    $"DriverType '{driverType}' factory already registered for this process");
+            _factories[driverType] = factory;
+        }
+    }
+
+    /// <summary>
+    ///     Try to look up the factory for <paramref name="driverType"/>. Returns null
+    ///     if no driver assembly registered one — bootstrapper logs + skips so a
+    ///     missing-assembly deployment doesn't take down the whole server.
+    /// </summary>
+    public Func<string, string, IDriver>? TryGet(string driverType)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverType);
+        lock (_lock) return _factories.GetValueOrDefault(driverType);
+    }
+
+    public IReadOnlyCollection<string> RegisteredTypes
+    {
+        get { lock (_lock) return [.. _factories.Keys]; }
+    }
+}