Make the per-owner project cap configurable via env

Self-hosters shouldn't be stuck with a hardcoded 100-project limit;
MAX_PROJECTS_PER_OWNER now controls it, defaulting to 0 (unlimited).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/ProjectTest.php

@@ -39,8 +39,9 @@ final class ProjectTest extends ApiTestCase
         self::assertSame(['apple', 'Banana', 'Cherry'], $titles);
     }
 
-    public function test_an_owner_cannot_exceed_100_projects(): void
+    public function test_an_owner_cannot_exceed_the_configured_project_limit(): void
     {
+        $this->reconfigure(['MAX_PROJECTS_PER_OWNER' => '100']);
         $auth = $this->authHeader();
 
         for ($i = 1; $i <= 100; $i++) {