Cross-platform NegotiateAuthentication; StorageType field; docs polish

HistorianSspiClient rewritten on top of System.Net.Security.NegotiateAuthentication
in place of P/Invoke into secur32.dll's InitializeSecurityContextW. The class
keeps the same Next() / Dispose() / two-constructor surface so callers don't
change. RequiredProtectionLevel=EncryptAndSign + AllowedImpersonationLevel=
Identification produces a request-flag set equivalent to the captured native
0x2081C / 0x81C bitmasks (still preserved as constants for the existing unit
tests). Removes the only Windows P/Invoke in the production SDK; the
[SupportedOSPlatform("windows")] gating elsewhere stays in place pending a
separate sweep.

HistorianStorageType (Cyclic = 1, Delta = 2):
Captured 2026-05-04 via --write-storage-type on the harness. Delta differs
from Cyclic in three places — header byte 10 (0x02 -> 0x06), flag-block
byte 1 (0x01 -> 0x02), and 4 zero bytes inserted after StorageRate before
the FILETIME. Server persists Tag.StorageType=1/2 accordingly. Plumbed
through HistorianTagDefinition.StorageType + serializer + orchestrator + 2
new tests (golden bytes + live SQL persistence verification).

Docs polish:
CLAUDE.md no longer claims "no P/Invoke" (HistorianSspiClient is the one
allowed P/Invoke surface); updated test count to 169+; AGENTS.md Required
SDK Surface and Repository Layout brought up to date with the live state
including the write surface; handoff.md "not a git working tree" obsolete
note removed.

171/171 tests pass with the NegotiateAuthentication replacement (was 169;
+2 new tests for StorageType).

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

tools/AVEVA.Historian.NativeTraceHarness/Program.cs

@@ -238,6 +238,7 @@ internal static class Program
             bool skipAddTag = HasFlag(args, "--write-skip-add-tag");
             bool skipAddValue = HasFlag(args, "--write-skip-add-value");
             bool writeApplyScaling = HasFlag(args, "--write-apply-scaling");
+            string writeStorageTypeName = GetArg(args, "--write-storage-type") ?? "Cyclic";
 
             // Decoded via dnlib — actual enum field types on HistorianTag:
             //   set_TagDataType    stfld ArchestrA.HistorianDataType    HistorianTag::dataType
@@ -255,7 +256,7 @@ internal static class Program
             SetProperty(tag, "TagDescription", "SDK write-RE sandbox tag");
             SetProperty(tag, "EngineeringUnit", "test");
             SetProperty(tag, "TagDataType", Enum.Parse(tagDataTypeEnum, writeDataTypeName, ignoreCase: true));
-            SetProperty(tag, "TagStorageType", Enum.Parse(tagStorageTypeEnum, "Cyclic", ignoreCase: true));
+            SetProperty(tag, "TagStorageType", Enum.Parse(tagStorageTypeEnum, writeStorageTypeName, ignoreCase: true));
             SetProperty(tag, "MinEU", writeMinEu);
             SetProperty(tag, "MaxEU", writeMaxEu);
             SetProperty(tag, "MinRaw", writeMinRaw);