docs(alarms): document the Alarms accessor + AckTime, tick MES plan Phase 1

Design doc and code travel together (CLAUDE.md editing rules), so this records
what the two preceding commits shipped and, more usefully, WHY the non-obvious
choices were made -- the parts a future reader would otherwise re-litigate:

  - Component-SiteRuntime.md: the Alarms.CurrentAsync() runtime API entry (why
    it is not scope-prefixed, why it is read-only, why placeholder rows are
    included), the full ScriptAlarm shape, AckTime on the enriched
    AlarmStateChanged, proto field 24, and the metadata_json-vs-new-column
    persistence rationale (native_alarm_state is RegisterReplicated; LocalDb
    builds its CDC triggers from the column list at registration time).
  - Component-DataConnectionLayer.md already carried the AckTime section in the
    first commit; this adds the SiteRuntime/ScriptAnalysis/InboundAPI halves.
  - Component-ScriptAnalysis.md: accessors returning domain types return the
    SAME type on both surfaces, and the trust-model note that a deny-list needs
    no entry for a new globals member -- only that its return type resolves in
    a permitted namespace.
  - Component-InboundAPI.md records the NEGATIVE decision: there is
    deliberately no Route.To(...).GetAlarms(...) verb. Alarm state is
    per-instance and lives on the site's Instance Actor, so the read goes
    through a routed site script and the filtering happens where the data is;
    central stays a thin router.
  - CLAUDE.md native-alarm bullet gains the enrichment + accessor summary.
  - The plan's §7 Phase 1 rows are ticked with 2026-08-01 and annotated with
    what was actually built (incl. the two choices that differ from the plan's
    "or" options: a dedicated snapshot message rather than DebugSnapshotRequest,
    and the extra SandboxScriptHost mirror the plan did not list). Phases 2-4
    stay open -- they are deployed config and need a live rig.

CLAUDE.md

@@ -98,6 +98,7 @@ spec for each is `docs/requirements/Component-<Name>.md`, and `README.md` carrie
 - **The gRPC boundary is authenticated (PSK) as of 2026-07-22; Akka remoting still is not, and nothing is encrypted.** Akka remoting sets no `enable-ssl`, no secure cookie, no `trusted-selection-paths` — so intra-cluster Akka remoting remains open to anyone who can reach the remoting port, and that boundary still assumes a trusted network. The gRPC listener stays **h2c**, but `SiteStreamService` is no longer open: `ControlPlaneAuthInterceptor` (`Host/ControlPlaneAuthInterceptor.cs`) gates `/sitestream.SiteStreamService/` — including the `PullAuditEvents`/`PullSiteCalls` RPCs that return audit rows — against a **per-site preshared key**, fail-closed, constant-time compared, alongside the separate `LocalDbSyncAuthInterceptor` on `/localdb_sync.v1.LocalDbSync/` with its own separate key. **Site side:** `ScadaBridge:Communication:GrpcPsk`, in production `${secret:SB-GRPC-PSK-<siteId>}`, and **`StartupValidator` refuses to boot a site node without it** (an unset key would leave the node healthy-looking but serving nothing). **Central side:** `SitePskProvider` resolves `SB-GRPC-PSK-{siteId}` from the secrets store at channel-build time (sites are added at runtime, so no boot-time expansion is possible), with `ScadaBridge:Communication:SitePsks:{siteId}` as an override for hosts running without a master key — the docker rig uses the latter. One key per site, never fleet-wide. A bearer token over h2c is readable and replayable on-path; TLS is the follow-on hardening and needs no change to this design. Introduced by Phase 0 of the ClusterClient→gRPC migration (`docs/plans/2026-07-22-clusterclient-to-grpc-plan.md`).
 - gRPC streaming channel — **note the direction is inverted from the data flow**: data moves site→central, but each **site node hosts the gRPC server** (`SiteStreamGrpcServer`, Kestrel h2c, port 8083, mapped **only in the Site branch** of `Program.cs`) and **central is the client**, dialling in. Central creates per-site `SiteStreamGrpcClient` via `SiteStreamGrpcClientFactory`, keyed **`(siteId, endpoint)`** — the key was widened from site-only to fix an arch-review High where one session's NodeA→NodeB flip disposed a channel another session was still using. Proto evolution is **additive only** and field numbers are never reused (`AlarmStateUpdate` grew 7→23 fields for the native-alarm mirror). Generated C# is **vendored** under `Communication/SiteStreamGrpc/` with the `<Protobuf>` include commented out — regeneration is a manual toggle-build-copy-untoggle.
 - Native alarms are a **read-only** mirror of OPC UA Alarms & Conditions and MxAccess Gateway alarms — **no ack-back, no central tables**; state lives in the site's `native_alarm_state`, survives failover, and is cleared on redeploy/undeploy (mirrors static overrides). Central's per-site live alarm cache (`ISiteAlarmLiveCache`) is **transient in-memory only** — there is deliberately no persisted central alarm store, so the 15s poll remains the NotReporting authority behind the live stream. See `Component-DataConnectionLayer.md` / `Component-CentralUI.md` for the model and the authoring surface.
+  - **`AckTime` mirror enrichment + the `Alarms` script accessor (MES alarm-status API Phase 1, 2026-08-01).** `AlarmStateChanged` carries an additive `AckTime` (`DateTimeOffset?`), mirrored on the vendored `AlarmStateUpdate` proto as **field 24** and persisted inside `native_alarm_state`'s `metadata_json` — deliberately NOT a new column, because that table is `RegisterReplicated` and LocalDb builds its CDC triggers from the column list at registration time. Set only while a condition is active AND acknowledged (so it is null while unacked and cleared on re-raise); the DCL stamps the source's own ack instant for OPC UA (new SelectClause **index 18** = `AckedState/TransitionTime`) and its observation time of the ack transition for MxGateway, which supplies none. Site `Call` scripts read alarms via the new **`Alarms.CurrentAsync()`** accessor (`ScriptRuntimeContext` + `ScriptGlobals`, local Ask on `GetAlarmSnapshotRequest`, returns `Commons.Types.Scripts.ScriptAlarm`), mirrored on `ScriptCompileSurface` AND the Central UI `SandboxScriptHost` editor surface. The trust model needed no change — it is a deny-list over API roots, not an allow-list of context members. Plan: `docs/plans/2026-06-30-mes-alarm-status-api.md` (Phases 2–4 are deployed config, not repo).
 - OPC UA cert trust is **site-local and not persisted centrally** (follow-up): the verify-endpoint probe captures an untrusted server cert but **NEVER trusts it**, and DeploymentManager broadcasts `TrustServerCertCommand`/`RemoveServerCertCommand` to **BOTH** site nodes — `CertStoreActor` runs on every site node, not as a singleton, so PKI stores stay consistent across failover.
 
 ### External Integrations