Migrate frontend to TypeScript with Deno-based tooling (#206)

Compiles assets/*.ts via sensiolabs/typescript-bundle (standalone SWC
binary) and adds Deno for formatting, linting, type-checking, and
tests, keeping the project's no-Node/npm approach intact. Wires all
four into CI, the Justfile, and the pre-commit hook.

importmap.php

@@ -25,8 +25,8 @@ declare(strict_types=1);
  * }>
  */
 return [
-    'quiz' => ['path' => './assets/quiz.js', 'entrypoint' => true],
-    'backoffice' => ['path' => './assets/backoffice.js', 'entrypoint' => true],
+    'quiz' => ['path' => './assets/quiz.ts', 'entrypoint' => true],
+    'backoffice' => ['path' => './assets/backoffice.ts', 'entrypoint' => true],
     '@symfony/stimulus-bundle' => ['path' => './vendor/symfony/stimulus-bundle/assets/dist/loader.js'],
     'bootstrap' => ['version' => '5.3.8'],
     '@popperjs/core' => ['version' => '2.11.8'],