demo: MySQL env policy and gitignore (REQ-DEMO-011)

Author: HecFranco

demo/symfony8/.env.test

@@ -7,4 +7,4 @@ KERNEL_CLASS='App\Kernel'
 APP_SECRET=test_secret
 
 # DATABASE_URL: isolated SQLite database for demo tests.
-DATABASE_URL="sqlite:///%kernel.project_dir%/var/test.db"
+DATABASE_URL=mysql://app:app@db:3306/app?serverVersion=8.4&charset=utf8mb4

demo/symfony8/.gitignore

@@ -30,3 +30,8 @@
 *.tgz
 *.rar
 *.7z
+
+# SQLite artifacts (REQ-DEMO-011 — demos use MySQL)
+*.db
+*.sqlite
+*.sqlite3