test(api): wire up real mysqli in SchemaHealthCheckTest (TRU-77 unit CI)

The Unit suite starts with a freshly-dropped test database and does
not create a $db global, so:

- customer_invoice_email_schema_bootstrap::ensureSchema() short-
  circuited and never created the users table.
- runSchemaCheck had nothing to inspect and reported ok=false.

Wire up a real mysqli connection at file load time using the same
CONFIG_DB_* env vars the rest of the CI suite exports, then have
beforeEach run the bootstrap and create the bare-minimum invoices /
bookings tables that runSchemaCheck verifies. This keeps the test
self-contained inside the Unit suite without changing the
production code or the production schema.

Refs: api#383, TRU-77

services/nginx/app/tests/Unit/SchemaHealthCheckTest.php

@@ -12,6 +12,8 @@
  * endpoint in `adminRoute.php` which the deploy pipeline hits.
  */
 
+app_require('classes/customer_invoice_email_schema_bootstrap.php');
+
 use classes\customer_invoice_email_schema_bootstrap;
 
 const REQUIRED_USERS_COLUMNS = [
@@ -28,13 +30,130 @@ const REQUIRED_USERS_COLUMNS = [
     'created_at',
 ];
 
+/**
+ * The unit test bootstrap does not create a $db global. This contract
+ * test is unique in that it needs a real database to verify schema
+ * state, so wire one up here using the same CONFIG_DB_* env vars the
+ * rest of the CI suite exports. If the database is unavailable, the
+ * tests below will fail with a clear "no_db_connection" error.
+ */
+schema_health_check_test_wire_db();
+
+function schema_health_check_test_wire_db(): void
+{
+    if (isset($GLOBALS['db']) && is_object($GLOBALS['db'])) {
+        return;
+    }
+    if (!class_exists('mysqli')) {
+        return;
+    }
+
+    $host = (string)(getenv('CONFIG_DB_HOST') ?: 'mysql-debug');
+    $user = (string)(getenv('CONFIG_DB_USER') ?: 'root');
+    $password = (string)(getenv('CONFIG_DB_PASSWORD') ?: 'debug_root_password');
+    $database = (string)(getenv('CONFIG_DB_DATABASE') ?: 'nnks_db_debug');
+    $port = (int)(getenv('CONFIG_DB_PORT') ?: 3306);
+
+    try {
+        mysqli_report(MYSQLI_REPORT_OFF);
+        $conn = new mysqli($host, $user, $password, $database, $port);
+        if ($conn->connect_errno) {
+            return;
+        }
+        $conn->set_charset('utf8mb4');
+    } catch (\Throwable $e) {
+        return;
+    }
+
+    $GLOBALS['db'] = new class($conn) {
+        private mysqli $conn;
+
+        public function __construct(mysqli $conn)
+        {
+            $this->conn = $conn;
+        }
+
+        public function query(string $sql)
+        {
+            return $this->conn->query($sql);
+        }
+
+        public function fetch_assoc($result)
+        {
+            return $result ? $result->fetch_assoc() : null;
+        }
+
+        public function close(): void
+        {
+            try {
+                $this->conn->close();
+            } catch (\Throwable) {
+            }
+        }
+    };
+}
+
+/**
+ * The unit suite starts with a freshly-dropped `nnks_db_debug` database
+ * (see run_ci_suite::reset_ci_state). The schema bootstrap only owns
+ * the `users` table; `invoices` and `bookings` are managed by other
+ * migrations that don't run in the unit suite. Create the bare-minimum
+ * schema that adminRoute::runSchemaCheck needs so the third test can
+ * verify the "all columns exist" happy path.
+ */
+function schema_health_check_test_ensure_aux_tables(): void
+{
+    global $db;
+    if (!isset($db) || !is_object($db) || !method_exists($db, 'query')) {
+        return;
+    }
+
+    $create = function (string $table, string $createSql, array $requiredColumns) use ($db): void {
+        $r = $db->query("SHOW TABLES LIKE '{$table}'");
+        if (!$r || (int)$r->num_rows === 0) {
+            $db->query($createSql);
+            return;
+        }
+        foreach ($requiredColumns as $column => $definition) {
+            $r = $db->query("SHOW COLUMNS FROM `{$table}` LIKE '{$column}'");
+            if (!$r || (int)$r->num_rows === 0) {
+                $db->query("ALTER TABLE `{$table}` ADD COLUMN `{$column}` {$definition}");
+            }
+        }
+    };
+
+    $create('invoices', "CREATE TABLE `invoices` (
+        id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+        customer_number INT NOT NULL DEFAULT 0,
+        po_number VARCHAR(64) NULL,
+        closed_at DATETIME NULL
+    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci", [
+        'po_number' => 'VARCHAR(64) NULL',
+        'closed_at' => 'DATETIME NULL',
+        'customer_number' => 'INT NOT NULL DEFAULT 0',
+    ]);
+
+    $create('bookings', "CREATE TABLE `bookings` (
+        id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+        customer_number INT NOT NULL DEFAULT 0,
+        department INT NULL
+    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci", [
+        'customer_number' => 'INT NOT NULL DEFAULT 0',
+        'department' => 'INT NULL',
+    ]);
+}
+
 beforeEach(function () {
     // Self-heal: run the schema bootstrap so the test DB has all
     // the columns the contract requires. The bootstrap is additive
     // and idempotent — safe to run on every test.
+    if (!isset($GLOBALS['db']) || !is_object($GLOBALS['db'])) {
+        schema_health_check_test_wire_db();
+    }
     if (class_exists(customer_invoice_email_schema_bootstrap::class)) {
         customer_invoice_email_schema_bootstrap::ensureSchema();
     }
+    schema_health_check_test_ensure_aux_tables();
 });
 
 it('users table has every required column the code references', function () {