fix(address-space): no UNS value Variable for a reference to an alarm-bearing tag (#896)

A UnsTagReference to a raw tag that carries an "alarm" object produced a UNS
value Variable that read BadWaitingForInitialData forever (G6 live gate,
TestAlarm002Condition on testmachine-015). BuildUnsReferenceVariables now skips
those references; the equipment gets the alarm only as the raw condition wired
as an event notifier of its folder, which is unchanged (the reference still
feeds RawTagPlan.ReferencingEquipmentPaths).

Why condition-only and not "feed the mirror":
- The raw side has no value node for such a tag: AddressSpaceApplier
  materialises an alarm tag as a condition OR a value variable, never both.
  There is no raw value for the UNS mirror to mirror.
- DriverHostActor skips alarm tags when it builds the value fan-out and write
  routing maps (`continue` before the UNS registration), and the driver leaves
  them out of its value subscription ("subscribed to 5 refs" with 6 tags in
  G6). Feeding the mirror would mean subscribing a value the design says the
  tag does not have.
- Docs already state condition-only: ScriptedAlarms.md ("instead of a value
  variable"), AlarmTracking.md ("only the condition, with no sibling value
  variable"), the v3 design (native alarm = one condition at the raw tag,
  surfaced at equipment via notifiers).
- The composer tests that asserted the mirror were incidental: f4f3e17e
  (v3 B4-WP1) put the alarm on the fixture's Speed tag to test raw alarm
  attachment, and later tests reused Speed for writable / historian / array
  checks of the mirror. No commit or doc chose a value mirror for alarm tags.
- ScadaBridge does not read it: its OtOpcUa alarm path is event subscriptions
  on the equipment/raw folders (v3 alarm B/C live gate), and a node that never
  had a value cannot be a working binding. G6 itself authored the alarm's
  Boolean as a separate value tag (TestAlarm002), which is the supported way to
  read it.

Tests: the composer fixture moves the alarm onto its own HighTemp tag
(Speed is now a plain historized value tag), with a new test asserting no UNS
Variable for the alarm reference, with positive controls (the raw tag still
carries the equipment path; the value references still emit). New real-SDK
test Alarm_bearing_reference_surfaces_as_the_condition_only_against_real_SDK:
no Variable at the UNS path, the Speed mirror present, one condition, the
equipment folder wired as its notifier. Both new tests fail with the skip
removed. Docs: Uns.md, ScriptedAlarms.md, G6 evidence note.

Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi

docs/ScriptedAlarms.md

@@ -240,7 +240,9 @@ blob and is parsed byte-parity in both the compose (`AddressSpaceComposer`) and
 > never one-per-root. Teardown is symmetric (`RemoveNotifier(..., bidirectional:true)` on
 > rebuild / reference removal) so inverse-notifier entries never leak across redeploys.
 > Ack/confirm/shelve route on **`ConditionId = RawPath`** (never `SourceNodeId`), and the
-> `/alerts` row lists the referencing equipment paths. See
+> `/alerts` row lists the referencing equipment paths. The equipment gets the condition
+> **only**: no UNS value variable is created for a reference to an alarm-bearing tag (#896),
+> matching the raw side, which has no value variable either. See
 > [AlarmTracking.md](AlarmTracking.md) and the WP4 section of
 > `docs/plans/2026-07-15-v3-batch4-address-space-plan.md`.