Phase 6.2 Stream C — Call + Alarm Acknowledge/Confirm gating

Closes task #122 (Acknowledge + Confirm + generic Call — Shelve stays as
a follow-up pending per-instance method-NodeId resolution).

Before this commit any session with a connected channel could invoke
method nodes on driver-materialized equipment — including alarm
Acknowledge / Confirm. Combined with the Browse + CreateMonitoredItems
gates that landed earlier in Stream C, this was the last service-layer
entry point where a session could still affect state without passing
the authz trie.

Implementation on DriverNodeManager:
- `Call` override — pre-iterates methodsToCall, gates each through
  AuthorizationGate with the operation kind returned by
  MapCallOperation. Denied calls get errors[i] = BadUserAccessDenied
  before delegating to base.Call.
- `MapCallOperation(NodeId methodId)` — maps well-known Part 9 method
  NodeIds to dedicated operation kinds:
    MethodIds.AcknowledgeableConditionType_Acknowledge →
        OpcUaOperation.AlarmAcknowledge
    MethodIds.AcknowledgeableConditionType_Confirm →
        OpcUaOperation.AlarmConfirm
    everything else → OpcUaOperation.Call
  Lets the ACL distinguish "can acknowledge alarms" from "can invoke
  arbitrary methods" without conflating the two roles.
- Shelve dispatch paths through per-instance ShelvedStateMachine methods
  with dynamic NodeIds that can't be constant-matched — falls through
  to generic Call. Fine-grained OpcUaOperation.AlarmShelve is a follow-
  up when the method-invocation path grows a "method-role" annotation.

Extracted GateCallMethodRequests + MapCallOperation as static internal
for unit-testability. 8 new tests (MapCallOperation Acknowledge /
Confirm / generic; gate-null no-op, denied-Acknowledge, allowed-
Acknowledge, mixed-batch, pre-populated-error-preserved).
Server.Tests 269 → 277.

Known follow-ups:
- Shelve per-operation gating (see above).
- TranslateBrowsePathsToNodeIds gating (Browse follow-up from #120).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/v2/v2-release-readiness.md

@@ -36,8 +36,8 @@ Remaining Stream C surfaces (hardening, not release-blocking):
 
 - ~~Browse + TranslateBrowsePathsToNodeIds gating with ancestor-visibility logic per `acl-design.md` §Browse.~~ **Partial, 2026-04-24.** `DriverNodeManager.Browse` override post-filters the `ReferenceDescription` list via a new `FilterBrowseReferences` helper — denied nodes disappear silently per OPC UA convention. Ancestor-visibility implication (Read-grant at `Line/Tag` implying Browse on `Line`) still to ship; needs a subtree-has-any-grant query on the trie evaluator. `TranslateBrowsePathsToNodeIds` surface not yet wired.
 - ~~CreateMonitoredItems + TransferSubscriptions gating with per-item `(AuthGenerationId, MembershipVersion)` stamp so revoked grants surface `BadUserAccessDenied` within one publish cycle (decision #153).~~ **Partial, 2026-04-24.** `DriverNodeManager.CreateMonitoredItems` override pre-gates each request and pre-populates `BadUserAccessDenied` into the errors slot for denied items (the base stack honours pre-set errors and skips those items). Decision #153's per-item `(AuthGenerationId, MembershipVersion)` stamp for detecting mid-subscription revocation is still to ship — needs subscription-layer plumbing. TransferSubscriptions not yet wired (same pattern).
-- Alarm Acknowledge / Confirm / Shelve gating.
-- Call (method invocation) gating.
+- ~~Alarm Acknowledge / Confirm / Shelve gating.~~ **Partial, 2026-04-24.** Acknowledge + Confirm map to dedicated `OpcUaOperation.AlarmAcknowledge` / `AlarmConfirm` via `MapCallOperation`; Shelve falls through to generic `OpcUaOperation.Call` (needs per-instance method NodeId resolution to distinguish — follow-up).
+- ~~Call (method invocation) gating.~~ **Closed 2026-04-24.** `DriverNodeManager.Call` override pre-gates each `CallMethodRequest` via `GateCallMethodRequests`. Denied calls return `BadUserAccessDenied` without running the method. Alarm methods map to alarm-specific operation kinds; everything else gates as generic `Call`.
 - Finer-grained scope resolution — current `NodeScopeResolver` returns a flat cluster-level scope. Joining against the live Configuration DB to populate UnsArea / UnsLine / Equipment path is tracked as Stream C.12.
 - 3-user integration matrix covering every operation × allow/deny.