5402: Roll back PHP 8.4 and Psalm 6 update

Revert phpfpm image to itkdev/php8.3-fpm and pin vimeo/psalm back to
^5.12.0. Restore composer.lock and symfony.lock to the release/3.0.0
state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: turegjorup

composer.json

@@ -63,7 +63,7 @@
         "symfony/stopwatch": "~6.4.0",
         "symfony/var-dumper": "~6.4.0",
         "symfony/web-profiler-bundle": "~6.4.0",
-        "vimeo/psalm": "^6.13.0",
+        "vimeo/psalm": "^5.12.0",
         "vincentlanglet/twig-cs-fixer": "^3.8",
         "weirdan/doctrine-psalm-plugin": "^2.0"
     },