docs(historian): fix-wave docs and stale comments

- Historian.md: Empty samples always Bad (writer/updater/read clamp),
  long-name refusal, 5 s bootstrap failure cache, AtTime after now, info-bit
  masking, HistoryUpdate does NOT type-check (M-1 decision), DeleteRaw
  needs both bounds, reverse Raw paging, the historian/historization metric
  prefixes, and provisioning numeric-only lines qualified as Gateway.
- CLAUDE.md numeric-only lines qualified as Gateway backend.
- Stale 'sole historian' lines in DriverLifecycle, ServiceHosting and the
  retired Wonderware stub; Client.CLI exit-code contract.
- ServerHistorianOptions: Endpoint/Backend XML docs untangled, Validate()
  indented; Program.cs comments are backend-neutral; T10 week-test day count.

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

docs/DriverLifecycle.md

@@ -620,8 +620,9 @@ Implementation:
   `GatewayAlarmHistorianWriter` (the gateway `SendEvent` path; see
   [AlarmHistorian.md](AlarmHistorian.md)).
 
-The HistorianGateway is the sole historian backend; its config keys and
-deployment prerequisites are in [Historian.md](Historian.md).
+The historian backend is pluggable (`ServerHistorian:Backend` = `Gateway`, the default, or `SqlServer`);
+the HistorianGateway is the Gateway backend. Config keys and deployment prerequisites for both are in
+[Historian.md](Historian.md).
 
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