feat(test): add multi-engine integration matrix

tests/bootstrap.php

@@ -5,12 +5,52 @@
 
 require_once __DIR__ . '/../vendor/autoload.php';
 
+// Engine selection: DUCKBRAIN_TEST_DB=sqlite|mysql|pgsql (default: sqlite).
+// sqlite uses an in-memory database, so the unit suite never needs services.
+$engine = strtolower(getenv('DUCKBRAIN_TEST_DB') ?: 'sqlite');
+
+$profiles = [
+    'sqlite' => [
+        'type' => 'sqlite',
+        'host' => 'localhost',
+        'name' => ':memory:',
+        'user' => '',
+        'pass' => '',
+    ],
+    'mysql' => [
+        'type' => 'mysql',
+        'host' => '127.0.0.1',
+        'name' => 'duckbrain_test',
+        'user' => 'duckbrain',
+        'pass' => 'duckbrain',
+    ],
+    'pgsql' => [
+        'type' => 'pgsql',
+        'host' => '127.0.0.1',
+        'name' => 'duckbrain_test',
+        'user' => 'duckbrain',
+        'pass' => 'duckbrain',
+    ],
+];
+
+if (!isset($profiles[$engine])) {
+    fwrite(
+        STDERR,
+        "Invalid DUCKBRAIN_TEST_DB '{$engine}'. Expected one of: "
+        . implode(', ', array_keys($profiles)) . "\n"
+    );
+    exit(1);
+}
+
 // Define DB constants BEFORE config.php so the test database wins over the
 // real configuration (config.php's define() warnings are suppressed by @).
-define('DB_TYPE', 'sqlite');
-define('DB_HOST', 'localhost');
-define('DB_NAME', ':memory:');
-define('DB_USER', '');
-define('DB_PASS', '');
+// Each field can be overridden without losing the engine's other defaults.
+$profile = $profiles[$engine];
+
+define('DB_TYPE', $profile['type']);
+define('DB_HOST', getenv('DUCKBRAIN_TEST_HOST') ?: $profile['host']);
+define('DB_NAME', getenv('DUCKBRAIN_TEST_NAME') ?: $profile['name']);
+define('DB_USER', getenv('DUCKBRAIN_TEST_USER') ?: $profile['user']);
+define('DB_PASS', getenv('DUCKBRAIN_TEST_PASS') ?: $profile['pass']);
 
 @require_once __DIR__ . '/../autoload.php';