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).

src/ScadaLink.StoreAndForward/StoreAndForwardStorage.cs

@@ -25,6 +25,8 @@ public class StoreAndForwardStorage
     /// </summary>
     public async Task InitializeAsync()
     {
+        EnsureDatabaseDirectoryExists();
+
         await using var connection = new SqliteConnection(_connectionString);
         await connection.OpenAsync();
 
@@ -53,6 +55,32 @@ public class StoreAndForwardStorage
         _logger.LogInformation("Store-and-forward SQLite storage initialized");
     }
 
+    /// <summary>
+    /// Ensures the directory for a file-backed SQLite database exists. SQLite creates
+    /// the database file on demand but not its parent directory, so a configured path
+    /// such as "./data/store-and-forward.db" fails to open ("unable to open database
+    /// file") when the "data" directory does not yet exist. In-memory databases and
+    /// bare filenames in the working directory have no directory to create and are
+    /// skipped.
+    /// </summary>
+    private void EnsureDatabaseDirectoryExists()
+    {
+        var builder = new SqliteConnectionStringBuilder(_connectionString);
+        if (builder.Mode == SqliteOpenMode.Memory)
+            return;
+
+        var dataSource = builder.DataSource;
+        if (string.IsNullOrEmpty(dataSource) || dataSource == ":memory:")
+            return;
+
+        var directory = System.IO.Path.GetDirectoryName(System.IO.Path.GetFullPath(dataSource));
+        if (!string.IsNullOrEmpty(directory) && !System.IO.Directory.Exists(directory))
+        {
+            System.IO.Directory.CreateDirectory(directory);
+            _logger.LogInformation("Created store-and-forward database directory: {Directory}", directory);
+        }
+    }
+
     /// <summary>
     /// WP-9: Enqueues a new message with Pending status.
     /// </summary>