fix(historian): ContinuousHistorization CommitMode code default is PerEntry, matching appsettings/docker-dev/fallback (lmxopcua#776)

The Lane H2 remediation made Periodic(100 ms) the options-class default, but
appsettings.json, docker-dev and Program.cs's bad-value fallback all used
PerEntry, so effective behaviour never changed and the docs contradicted the
shipped config. The options default is now PerEntry; Periodic stays opt-in
(<= CommitIntervalMs of crash loss in exchange for throughput). Program.cs now
uses ContinuousHistorizationOptions.ResolveCommitMode() so the fallback shares
the single DefaultCommitMode constant. docs/Historian.md updated.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -315,10 +315,7 @@ if (hasDriver)
         // outbox depth/dropped gauges here (once, on first resolution) keeps the live instance behind them.
         builder.Services.AddSingleton<IHistorizationOutbox>(_ =>
         {
-            var commitMode = Enum.TryParse<HistorizationCommitMode>(
-                continuousHistorizationOptions.CommitMode, ignoreCase: true, out var parsedMode)
-                ? parsedMode
-                : HistorizationCommitMode.PerEntry;
+            var commitMode = continuousHistorizationOptions.ResolveCommitMode();
             var outbox = new FasterLogHistorizationOutbox(
                 continuousHistorizationOptions.OutboxPath,
                 commitMode,

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/ContinuousHistorizationOptions.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Runtime.Historian;
 
@@ -38,20 +39,28 @@ public sealed class ContinuousHistorizationOptions
     public string OutboxPath { get; init; } = "";
 
     /// <summary>
-    ///     Outbox commit cadence: <c>Periodic</c> (the default) commits on a background timer every
-    ///     <see cref="CommitIntervalMs"/> ms (100 ms by default — a crash can lose at most the last interval of captured
-    ///     values); <c>PerEntry</c> fsyncs before each append returns (no loss window, one fsync per append). Parsed
-    ///     case-insensitively against <c>HistorizationCommitMode</c>.
+    ///     Outbox commit cadence: <c>PerEntry</c> (the default, and what the shipped <c>appsettings.json</c>, docker-dev
+    ///     and the unparseable-value fallback all use) fsyncs before each append returns — no loss window; <c>Periodic</c>
+    ///     is the opt-in throughput mode that commits on a background timer every <see cref="CommitIntervalMs"/> ms
+    ///     (100 ms by default), so a crash can lose at most the last interval of captured values. Parsed
+    ///     case-insensitively against <c>HistorizationCommitMode</c>; see <see cref="ResolveCommitMode"/>.
     ///     <para>
-    ///         <b>Why Periodic.</b> Under <c>PerEntry</c> every ingest append waits for an fsync, so ingestion is capped at
-    ///         <c>1 / fsync_latency</c> appends per second (50 drivers × 1 Hz on a 10 ms-fsync disk kept the recorder half
-    ///         busy; at 100+ bursts/s it fell behind for good). The recorder now appends off its mailbox and coalesces
-    ///         every burst waiting behind a slow append into one group commit, which helps <c>PerEntry</c> too — but it is
-    ///         still one fsync per group on the critical path. <c>PerEntry</c> remains available where no loss window is
-    ///         acceptable.
+    ///         <b>Trade-off.</b> Under <c>PerEntry</c> every ingest append waits for an fsync, so ingestion is capped at
+    ///         <c>1 / fsync_latency</c> appends per second — but the recorder appends off its mailbox and coalesces
+    ///         every burst waiting behind a slow append into one group commit, so it is one fsync per group, not per
+    ///         value. Set <c>Periodic</c> explicitly where higher ingest throughput matters more than a bounded
+    ///         (<c>&lt;= CommitIntervalMs</c>) crash-loss window.
     ///     </para>
     /// </summary>
-    public string CommitMode { get; init; } = "Periodic";
+    public string CommitMode { get; init; } = DefaultCommitMode.ToString();
+
+    /// <summary>The commit mode used when <see cref="CommitMode"/> is not set or cannot be parsed.</summary>
+    public const HistorizationCommitMode DefaultCommitMode = HistorizationCommitMode.PerEntry;
+
+    /// <summary>Parses <see cref="CommitMode"/> case-insensitively; an unparseable value falls back to
+    /// <see cref="DefaultCommitMode"/> so the fallback always agrees with the options default.</summary>
+    public HistorizationCommitMode ResolveCommitMode() =>
+        Enum.TryParse<HistorizationCommitMode>(CommitMode, ignoreCase: true, out var mode) ? mode : DefaultCommitMode;
 
     /// <summary>Periodic-mode commit cadence in milliseconds; must be positive when
     /// <see cref="CommitMode"/> is <c>Periodic</c>. Ignored under <c>PerEntry</c>.</summary>