Phase 7 follow-up #243 — CachedTagUpstreamSource + Phase7EngineComposer

Ships the composition kernel that maps Config DB rows (Script / VirtualTag /
ScriptedAlarm) to the runtime definitions VirtualTagEngine + ScriptedAlarmEngine
consume, builds the engine instances, and wires OnEvent → historian-sink routing.

## src/ZB.MOM.WW.OtOpcUa.Server/Phase7/

- CachedTagUpstreamSource — implements both Core.VirtualTags.ITagUpstreamSource and
  Core.ScriptedAlarms.ITagUpstreamSource (identical shape, distinct namespaces) on one
  concrete type so the composer can hand one instance to both engines. Thread-safe
  ConcurrentDictionary value cache with synchronous ReadTag + fire-on-write
  Push(path, snapshot) that fans out to every observer registered via SubscribeTag.
  Unknown-path reads return a BadNodeIdUnknown-quality snapshot (status 0x80340000)
  so scripts branch on quality naturally.
- Phase7EngineComposer.Compose(scripts, virtualTags, scriptedAlarms, upstream,
  alarmStateStore, historianSink, rootScriptLogger, loggerFactory) — single static
  entry point that:
  * Indexes scripts by ScriptId, resolves VirtualTag.ScriptId + ScriptedAlarm.PredicateScriptId
    to full SourceCode
  * Projects DB rows to VirtualTagDefinition + ScriptedAlarmDefinition (mapping
    DataType string → DriverDataType enum, AlarmType string → AlarmKind enum,
    Severity 1..1000 → AlarmSeverity bucket matching the OPC UA Part 9 bands
    that AbCipAlarmProjection + OpcUaClient MapSeverity already use)
  * Constructs VirtualTagEngine + loads definitions (throws InvalidOperationException
    with the list of scripts that failed to compile — aggregated like Streams B+C)
  * Constructs ScriptedAlarmEngine + loads definitions + wires OnEvent →
    IAlarmHistorianSink.EnqueueAsync using ScriptedAlarmEvent.Emission as the event
    kind + Condition.LastAckUser/LastAckComment for audit fields
  * Returns Phase7ComposedSources with Disposables list the caller owns

Empty Phase 7 config returns Phase7ComposedSources.Empty so deployments without
scripts / alarms behave exactly as pre-Phase-7. Non-null sources flow into
OpcUaApplicationHost's virtualReadable / scriptedAlarmReadable plumbing landed by
task #239 — DriverNodeManager then dispatches reads by NodeSourceKind per PR #186.

## Tests — 12/12

CachedTagUpstreamSourceTests (6):
- Unknown-path read returns BadNodeIdUnknown-quality snapshot
- Push-then-Read returns cached value
- Push fans out to subscribers in registration order
- Push to one path doesn't fire another path's observer
- Dispose of subscription handle stops fan-out
- Satisfies both Core.VirtualTags + Core.ScriptedAlarms ITagUpstreamSource interfaces

Phase7EngineComposerTests (6):
- Empty rows → Phase7ComposedSources.Empty (both sources null)
- VirtualTag rows → VirtualReadable non-null + Disposables populated
- Missing script reference throws InvalidOperationException with the missing ScriptId
  in the message
- Disabled VirtualTag row skipped by projection
- TimerIntervalMs → TimeSpan.FromMilliseconds round-trip
- Severity 1..1000 maps to Low/Medium/High/Critical at 250/500/750 boundaries
  (matches AbCipAlarmProjection + OpcUaClient.MapSeverity banding)

## Scope — what this PR does NOT do

The composition kernel is the tricky part; the remaining wiring is three narrower
follow-ups that each build on this PR:

- task #244 — driver-bridge feed that populates CachedTagUpstreamSource from live
  driver subscriptions. Without this, ctx.GetTag returns BadNodeIdUnknown even when
  the driver has a fresh value.
- task #245 — ScriptedAlarmReadable adapter exposing each alarm's current Active
  state as IReadable. Phase7EngineComposer.Compose currently returns
  ScriptedAlarmReadable=null so reads on Source=ScriptedAlarm variables return
  BadNotFound per the ADR-002 "misconfiguration not silent fallback" signal.
- task #246 — Program.cs call to Phase7EngineComposer.Compose with config rows
  loaded from the sealed-cache DB read, plus SqliteStoreAndForwardSink lifecycle
  wiring at %ProgramData%/OtOpcUa/alarm-historian-queue.db with the Galaxy.Host
  IPC writer from Stream D.

Task #240 (live OPC UA E2E smoke) depends on all three follow-ups landing.

src/ZB.MOM.WW.OtOpcUa.Server/ZB.MOM.WW.OtOpcUa.Server.csproj

@@ -30,6 +30,10 @@
 
     <ItemGroup>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.VirtualTags\ZB.MOM.WW.OtOpcUa.Core.VirtualTags.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms\ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian\ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian.csproj"/>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Analyzers\ZB.MOM.WW.OtOpcUa.Analyzers.csproj"
                           OutputItemType="Analyzer" ReferenceOutputAssembly="false"/>
     </ItemGroup>