Pin Composer platform to PHP 7.4 to match CI

Adds platform.php 7.4.0 to composer.json config so dependency
resolution always targets the minimum supported PHP version, and
regenerates the lock file — downgrading doctrine/instantiator from
2.1.0 (requires PHP ^8.4) to 1.5.0 (supports PHP 7.x).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: louwie17

composer.json

@@ -18,6 +18,9 @@
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true
         },
+        "platform": {
+            "php": "7.4.0"
+        },
         "audit": {
             "ignore": {
                 "PKSA-5jz8-6tcw-pbk4": "PHPUnit is a test-only dev dependency; advisory does not affect production code paths.",