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.Server/OpcUaServerService.cs

@@ -18,6 +18,7 @@ public sealed class OpcUaServerService(
     DriverHost driverHost,
     OpcUaApplicationHost applicationHost,
     DriverEquipmentContentRegistry equipmentContentRegistry,
+    DriverInstanceBootstrapper driverBootstrapper,
     Phase7Composer phase7Composer,
     IServiceScopeFactory scopeFactory,
     ILogger<OpcUaServerService> logger) : BackgroundService
@@ -37,6 +38,13 @@ public sealed class OpcUaServerService(
         // address space until the first publish, then the registry fills on next restart.
         if (result.GenerationId is { } gen)
         {
+            // Task #248 — register IDriver instances from the published DriverInstance
+            // rows BEFORE the equipment-content load + Phase 7 compose, so the rest of
+            // the pipeline sees a populated DriverHost. Without this step Phase 7's
+            // CachedTagUpstreamSource has no upstream feed + virtual-tag scripts read
+            // BadNodeIdUnknown for every tag path (gap surfaced by task #240 smoke).
+            await driverBootstrapper.RegisterDriversFromGenerationAsync(gen, stoppingToken);
+
             await PopulateEquipmentContentAsync(gen, stoppingToken);
 
             // Phase 7 follow-up #246 — load Script + VirtualTag + ScriptedAlarm rows,