feat: Phase II auto-write (WriteGuard, audit, auth) + WO-2~7 완료

Phase II:
- FfOperatorAction entity + ff_operator_action DDL/DbSet
- IFeedforwardWriteGuard + FeedforwardWriteGuard (SP bounds, grade C, transient, NaN)
- IFeedforwardAuditService + FeedforwardAuditService (raw ADO insert/query)
- FeedforwardSupervisor.AutoWriteAsync (per-stream OPC UA after Tick, rate-limited)
- FeedforwardConfigStore: advisory_only now read/writes DB, sp_node_id column
- FeedforwardController: auth (X-Kb-Token) on config/delete/write/audit;
  POST write/{id}/{key} manual SP write; GET audit; write results in MapColumn
- ff.js: token header, auto-write badge, per-stream write result, spNodeId, advisoryOnly
- ff.css: .ff-write-badge, .ff-write, .ff-write-err, .ff-wg-blocked
- Program.cs: register audit (Scoped) + write guard (Singleton)

WO-2~7 (build 0W/0E, test 22/22):
- PCT monitor, θ auto-tune, slow bias, front position indicator,
  total reflux recovery, config form expansion

tests/ExperionCrawler.Tests/FeedforwardBiasTests.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using ExperionCrawler.Core.Application.Feedforward;
+using ExperionCrawler.Infrastructure.Control;
+using Xunit;
+
+namespace ExperionCrawler.Tests;
+
+public class FeedforwardBiasTests
+{
+    private static ColumnConfig Cfg() => new()
+    {
+        Id = 1, Name = "C-BIAS", Enabled = true, FeedTag = "f", ProductKey = "P",
+        ScanSec = 2, BiasMaWindowSec = 20,   // 10 샘플 창
+        Streams = new[]
+        {
+            new StreamConfig { Key = "P", FlowTag = "p", Role = StreamRole.Commanded, Grade = Confidence.A, TargetCoeff = 0.95 },
+            new StreamConfig { Key = "D", FlowTag = "d", Role = StreamRole.LevelDriven, Grade = Confidence.B, TargetCoeff = 0.02 },
+            new StreamConfig { Key = "B", FlowTag = "b", Role = StreamRole.LevelDriven, Grade = Confidence.B, TargetCoeff = 0.03 },
+        }
+    };
+
+    // FEED 100 고정, P=95 → K_obs ≈ 0.95, D/B는 물질수지 충족용
+    private static PvSnapshot Snap() => new(
+        new TagSample("f", 100, true, DateTime.UtcNow), null, Array.Empty<TagSample>(),
+        new Dictionary<string, TagSample> {
+            ["P"] = new("p", 95, true, DateTime.UtcNow),
+            ["D"] = new("d", 2,  true, DateTime.UtcNow),
+            ["B"] = new("b", 3,  true, DateTime.UtcNow),
+        });
+
+    [Fact]
+    public void KObs_and_VLossMa_accumulate_in_steady_state()
+    {
+        var engine = new FeedforwardEngine();
+        var st = new ColumnState();
+        AdvisoryResult res = engine.Tick(Cfg(), Snap(), st, DateTime.UtcNow);
+        for (int i = 0; i < 20; i++) res = engine.Tick(Cfg(), Snap(), st, DateTime.UtcNow);
+
+        var p = res.Streams.First(s => s.Key == "P");
+        Assert.NotNull(p.KObsSuggest);
+        Assert.InRange(p.KObsSuggest!.Value, 0.94, 0.96);   // 95/100
+
+        Assert.NotNull(res.VLossMa);
+        Assert.InRange(res.VLossMa!.Value, -0.5, 0.5);      // 100-(95+2+3)=0
+    }
+}