align dev tooling with youngstartup conventions

require-dev: phpstan ^2.1 + strict rules, larastan ^3, php-cs-fixer
^3.91 + jubeki/laravel-code-style ^2.18, ide-helper ^3.7. add
phpstan.neon (level max, app/ scope) and .php-cs-fixer.dist.php
(jubeki preset, modifier_keywords rule). phpunit.xml mirrors
youngstartup (sqlite :memory:, bcrypt rounds 4, enforceTimeLimit).
gitignore picks up _ide_helper.php, *~, .php-cs-fixer.cache. drop
sail's phpactor.json line. composer scripts: drop npm bits from
setup/dev (frontend lives separately). composer test + stan +
cs:check all green on default scaffold.

backend/phpunit.xml

@@ -1,8 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="./vendor/phpunit/phpunit/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          colors="true"
+         enforceTimeLimit="true"
 >
     <testsuites>
         <testsuite name="Unit">
@@ -25,7 +26,6 @@
         <env name="CACHE_STORE" value="array"/>
         <env name="DB_CONNECTION" value="sqlite"/>
         <env name="DB_DATABASE" value=":memory:"/>
-        <env name="DB_URL" value=""/>
         <env name="MAIL_MAILER" value="array"/>
         <env name="QUEUE_CONNECTION" value="sync"/>
         <env name="SESSION_DRIVER" value="array"/>