refactor(virtualtags): retire dormant VirtualTagEngine/Source/Definition + TimerTriggerScheduler (#603)

TimerTriggerScheduler was welded to the engine and has no production consumer.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/ScriptEditor.md

@@ -203,9 +203,9 @@ prefix. The concrete implementation `ScriptTagCatalog` reads `Tag` +
 literal against `DriverInstanceActor.AttributeValuePublished.FullReference`,
 which is the `FullName` field from `Tag.TagConfig`
 (see `ScriptTagCatalog.ExtractFullNameFromTagConfig` + `EquipmentNodeWalker.ExtractFullName`).
-The UNS-path engine (`Core.VirtualTags.VirtualTagEngine`, keyed by the
-slash-joined `Enterprise/Site/Area/Line/Equipment/TagName` browse path) is
-dormant — it is not wired into the host — so UNS browse paths never resolve at
+The former UNS-path cascade engine (`Core.VirtualTags.VirtualTagEngine`, keyed by the
+slash-joined `Enterprise/Site/Area/Line/Equipment/TagName` browse path) was
+retired (#603) — it was never wired into the host — so UNS browse paths never resolve at
 runtime and are intentionally NOT offered as completions.
 
 The catalog is scoped per Blazor circuit; each call creates and disposes its own
@@ -233,8 +233,8 @@ deploy time. An unrelated `anything.GetTag("…")` no longer triggers it.
 
 **`SetVirtualTag` is a no-op in production.** The live single-tag evaluator
 (`RoslynVirtualTagEvaluator`) drops cross-tag `ctx.SetVirtualTag(...)` writes
-(logged); the cascade `VirtualTagEngine` that honours them is dormant (not wired
-into the host). So hover on a `ctx.SetVirtualTag("…")` path literal appends a
+(logged); the cascade engine that would have honoured them (`VirtualTagEngine`) was retired
+unwired (#603). So hover on a `ctx.SetVirtualTag("…")` path literal appends a
 note that the write is dropped in single-tag mode and will not take effect at
 runtime — the path completions still help author the literal, but the author is
 not misled into relying on a no-op. Making `SetVirtualTag` functional would