fix(store-and-forward): create the SQLite database directory on init (StoreAndForward-014)

StoreAndForwardStorage.InitializeAsync opened a SqliteConnection against the
configured SqliteDbPath (default ./data/store-and-forward.db) without ensuring
the parent directory exists. SQLite creates the database file but not its
directory, so when data/ was absent the connection failed with
"SQLite Error 14: unable to open database file" — aborting the site host's
RegisterSiteActors at StoreAndForwardService.StartAsync.

This was the root cause of the six failing SiteActorPathTests. Production
masked it because the Docker image / deployment creates data/.

InitializeAsync now calls EnsureDatabaseDirectoryExists, which parses the
connection string and creates the parent directory of a file-backed database
(in-memory databases and bare filenames are skipped).

Regression test InitializeAsync_FileInMissingDirectory_CreatesDirectory fails
against the pre-fix code. Host suite now 155/155 green (was 149/155).

tests/ScadaLink.StoreAndForward.Tests/StoreAndForwardStorageTests.cs

@@ -221,4 +221,31 @@ public class StoreAndForwardStorageTests : IAsyncLifetime, IDisposable
             Status = StoreAndForwardMessageStatus.Pending
         };
     }
+
+    [Fact]
+    public async Task InitializeAsync_FileInMissingDirectory_CreatesDirectory()
+    {
+        // SQLite creates the database file on demand but not its parent directory;
+        // the storage must create the directory itself or OpenAsync fails with
+        // "unable to open database file" (the cause of the SiteActorPathTests failures).
+        var directory = Path.Combine(Path.GetTempPath(), "sf-storage-test-" + Guid.NewGuid().ToString("N"));
+        var dbPath = Path.Combine(directory, "store-and-forward.db");
+        Assert.False(Directory.Exists(directory));
+
+        try
+        {
+            var storage = new StoreAndForwardStorage(
+                $"Data Source={dbPath}", NullLogger<StoreAndForwardStorage>.Instance);
+
+            await storage.InitializeAsync();
+
+            Assert.True(Directory.Exists(directory));
+            Assert.True(File.Exists(dbPath));
+        }
+        finally
+        {
+            if (Directory.Exists(directory))
+                Directory.Delete(directory, recursive: true);
+        }
+    }
 }