refactor(sf,site): both stores take ILocalDb instead of a connection string

Tasks 5 and 6 of the Phase 2 plan, committed together because their test
fallout is entangled — several fixtures construct both stores.

StoreAndForwardStorage and SiteStorageService now take ILocalDb. Connections
come from ILocalDb.CreateConnection(), which hands out an already-open,
pragma-configured connection carrying the zb_hlc_next() UDF the capture triggers
call; a raw connection would lack the UDF and every write to a replicated table
would fail closed. Deleted with the connection strings: S&F's
EnsureDatabaseDirectoryExists and its per-open busy_timeout pragma, and the site
service's BusyTimeoutFloorSeconds normalization — LocalDb owns all of it now.

DI: AddSiteRuntime's string overload is gone (nothing left to supply), so the
Host calls the no-arg form. ScadaBridge:Database:SiteDbPath and
StoreAndForwardOptions.SqliteDbPath survive only as the migrator's source
locations in Tasks 8/9.

Two things the plan did not anticipate, both worth reading:

1. FOUND A REAL LATENT DEFECT, from Phase 1, now fixed. The plan assumed
   directory creation simply moved to LocalDb along with file ownership. It did
   not: the LocalDb library never creates the parent directory, and
   SqliteLocalDb opens the file eagerly in its constructor — so a missing
   directory is a hard boot failure ("SQLite Error 14: unable to open database
   file"), not a degraded start. The default site config points at the RELATIVE
   path ./data/site-localdb.db, so any site node without a pre-existing data/
   directory fails to boot. The docker rig escapes only because its volume mount
   happens to create /app/data — a coincidence that would have hidden this until
   a bare-metal or fresh deployment. This has been latent since Phase 1 made
   LocalDb:Path required; deleting S&F's EnsureDatabaseDirectoryExists here
   would have widened it. Re-established the guarantee at the layer that now
   owns the path (SiteLocalDbDirectory.Ensure, called before AddZbLocalDb) and
   pinned it with SiteLocalDbDirectoryTests. Non-vacuity is not assumed: two
   tests written against the wrong assumption failed with exactly this
   SQLite Error 14 before the fix existed.

2. Test fallout was ~7x the plan's estimate. The plan named "fixtures" in one
   project; the constructor change actually reaches 40 files across 7 test
   projects, and most used Mode=Memory;Cache=Shared — which LocalDb has no
   equivalent for, so every one had to move to a real temp file. Rather than
   copy the Phase 1 TestLocalDb fixture into 7 projects, added a shared
   tests/ZB.MOM.WW.ScadaBridge.TestSupport library (not a test project) so the
   WAL-sidecar cleanup and the "real, not stubbed" rationale live in one place.

Retargeted rather than deleted, in both directions: the S&F WAL test now asserts
against the LocalDb-backed store (WAL genuinely is LocalDb's job), while the
directory-creation test moved to Host.Tests (that guarantee is NOT LocalDb's).
SiteStorageServiceTests.Initialize_EnablesWalJournalMode got the same treatment.
DeploymentManagerMediumFindingsTests induced a persistence failure via an
unopenable path, which no longer reaches the assertion since the fixture now
throws first; it induces the same failure shape via an uninitialized store.

Verified: full solution build 0 warnings; SiteRuntime 532, Host 318,
AuditLog 355, ExternalSystemGateway 142, HealthMonitoring 97,
StoreAndForward 153 — 1597 passed, 0 failed.

Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts

tests/ZB.MOM.WW.ScadaBridge.StoreAndForward.Tests/StoreAndForwardServiceTests.cs

@@ -1,6 +1,6 @@
-using Microsoft.Data.Sqlite;
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+using ZB.MOM.WW.ScadaBridge.TestSupport;
 
 namespace ZB.MOM.WW.ScadaBridge.StoreAndForward.Tests;
 
@@ -9,20 +9,17 @@ namespace ZB.MOM.WW.ScadaBridge.StoreAndForward.Tests;
 /// </summary>
 public class StoreAndForwardServiceTests : IAsyncLifetime, IDisposable
 {
-    private readonly SqliteConnection _keepAlive;
+    private readonly TestLocalDb _localDb;
     private readonly StoreAndForwardStorage _storage;
     private readonly StoreAndForwardService _service;
     private readonly StoreAndForwardOptions _options;
-    private readonly List<SqliteConnection> _extraKeepAlives = new();
+    private readonly List<TestLocalDb> _extraLocalDbs = new();
 
     public StoreAndForwardServiceTests()
     {
-        var dbName = $"SvcTests_{Guid.NewGuid():N}";
-        var connStr = $"Data Source={dbName};Mode=Memory;Cache=Shared";
-        _keepAlive = new SqliteConnection(connStr);
-        _keepAlive.Open();
+        _localDb = TestLocalDb.CreateTemp("SvcTests");
 
-        _storage = new StoreAndForwardStorage(connStr, NullLogger<StoreAndForwardStorage>.Instance);
+        _storage = new StoreAndForwardStorage(_localDb.Db, NullLogger<StoreAndForwardStorage>.Instance);
 
         _options = new StoreAndForwardOptions
         {
@@ -41,23 +38,29 @@ public class StoreAndForwardServiceTests : IAsyncLifetime, IDisposable
 
     public void Dispose()
     {
-        _keepAlive.Dispose();
-        foreach (var c in _extraKeepAlives) c.Dispose();
+        DisposeLocalDb(_localDb);
+        foreach (var db in _extraLocalDbs) DisposeLocalDb(db);
+    }
+
+    /// <summary>Disposes a local database, then removes its file and WAL sidecars.</summary>
+    private static void DisposeLocalDb(TestLocalDb localDb)
+    {
+        var path = localDb.Path;
+        localDb.Dispose();
+        TestLocalDb.DeleteFiles(path);
     }
 
     /// <summary>
-    /// Builds a fresh service over its own in-memory (shared-cache) SQLite so a test
-    /// can call StartAsync without racing the shared <c>_service</c>'s timer. The
-    /// keep-alive connection is tracked for disposal.
+    /// Builds a fresh service over its own local database so a test can call
+    /// StartAsync without racing the shared <c>_service</c>'s timer. The database
+    /// is tracked for disposal.
     /// </summary>
     private StoreAndForwardService CreateService(TimeSpan? retryTimerInterval = null)
     {
-        var connStr = $"Data Source=DeferTests_{Guid.NewGuid():N};Mode=Memory;Cache=Shared";
-        var keepAlive = new SqliteConnection(connStr);
-        keepAlive.Open();
-        _extraKeepAlives.Add(keepAlive);
+        var localDb = TestLocalDb.CreateTemp("DeferTests");
+        _extraLocalDbs.Add(localDb);
 
-        var storage = new StoreAndForwardStorage(connStr, NullLogger<StoreAndForwardStorage>.Instance);
+        var storage = new StoreAndForwardStorage(localDb.Db, NullLogger<StoreAndForwardStorage>.Instance);
         storage.InitializeAsync().GetAwaiter().GetResult();
 
         var options = new StoreAndForwardOptions
@@ -557,12 +560,10 @@ public class StoreAndForwardServiceTests : IAsyncLifetime, IDisposable
         // Build a service whose timer fires almost immediately, with a handler
         // that pauses in the middle of delivery so we can observe StopAsync's
         // wait behaviour.
-        var dbName = $"StopWait_{Guid.NewGuid():N}";
-        var connStr = $"Data Source={dbName};Mode=Memory;Cache=Shared";
-        using var keepAlive = new SqliteConnection(connStr);
-        keepAlive.Open();
+        var localDb = TestLocalDb.CreateTemp("StopWait");
+        _extraLocalDbs.Add(localDb);
 
-        var storage = new StoreAndForwardStorage(connStr, NullLogger<StoreAndForwardStorage>.Instance);
+        var storage = new StoreAndForwardStorage(localDb.Db, NullLogger<StoreAndForwardStorage>.Instance);
         await storage.InitializeAsync();
 
         var options = new StoreAndForwardOptions