[Examples] Store SQLite database in .sqlite directory

Move the SQLite vector database from var/ to .sqlite/ and ensure the
directory is created automatically. This keeps generated database files
in a gitignored hidden directory consistent with other dot-prefixed
data directories.

examples/rag/.gitignore

@@ -1 +1,2 @@
 .symfony-docs/
+.sqlite/

examples/rag/sqlite.php

@@ -28,7 +28,10 @@ use Symfony\Component\Uid\Uuid;
 require_once dirname(__DIR__).'/bootstrap.php';
 
 // initialize the store — file-based SQLite for persistence
-$pdo = new PDO('sqlite:'.__DIR__.'/var/vectors.db');
+if (!is_dir(__DIR__.'/.sqlite')) {
+    mkdir(__DIR__.'/.sqlite', 0777, true);
+}
+$pdo = new PDO('sqlite:'.__DIR__.'/.sqlite/vectors.db');
 $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 $store = new Store($pdo, 'movies');
 $store->setup();