chore: adopt shared Guiding Light configs and fix conformance gaps

Brings preauth from 18/34 to 30/34 conformance (auth-gateway profile). The
remaining four checks all depend on files this branch cannot change (see below).

PHP toolchain (§1)
  - require.php  >=8.4 -> ^8.5, and pin config.platform to 8.5.0. The old
    constraint also permitted PHP 9, which is not a promise we can keep.
    composer.lock regenerated with --lock: content-hash + platform-overrides
    only, zero dependency version movement.
  - friendsofphp/php-cs-fixer  * -> ^3.95. A wildcard meant CI was not
    reproducible.

PHPStan (§2.2)
  - vendor the shared phpstan.neon.dist (level 6) + a generated baseline.
    187 errors are captured rather than fixed; the baseline should only shrink
    from here.
  - add phpstan/phpstan:^2.1 to require-dev.

Code style (§8.2)
  - vendor the shared .php-cs-fixer.dist.php (@Symfony + @Symfony:risky +
    declare_strict_types) and apply it: 59 of 67 files reformatted.
  - Verified this is a formatting change, not a behaviour change: all 313 tests
    pass after the reformat, all in_array() calls already passed strict=true,
    and the remaining edits are @Symfony:risky idiom (yoda conditions, \count(),
    self:: over the class name).

Repository layout (§4.4)
  - docs/{Caddyfile,compose.yaml,example.env} -> docs/examples/, with
    example.env becoming the conventional .env.example. This is the layout
    GUIDING-LIGHT already cites preauth as doing correctly — it just needed
    renaming.
  - update the four readme.md references and a stale compose.yaml comment.
  - docs/v1.1-plan.md references are left alone deliberately: it is a historical
    plan recording what was done at the time, not live documentation.

Licence and security policy (§7)
  - add LICENSE (uniform MIT, matching composer.json).
  - add SECURITY.md describing the actual threat model: per-request
    allow/intercept, no caching of the login flow, app-set security headers,
    TOTP, and the fact that REMOTE_USER is trusted input.

Mobile accessibility (§3.3a)
  - templates/base.html.twig: drop maximum-scale=1 and add viewport-fit=cover.
    preauth was the one app already past the font-size precondition (controls
    render at 21.6px = 0.9em x 24px), so removing the lock is safe here and
    restores pinch-zoom for Android users.

Conformance tooling (§8.2)
  - vendor .ci/conformance.sh and .ci/css-control-size.py so the check runs
    from a checkout rather than fetching from the LAN-only private/ci.
  - .editorconfig synced from the version that keeps the Caddyfile tab rule.

Not included (blocked by the .gitea/workflows pre-receive hook):
  - ci-composer-audit, ci-composer-validate, ci-reusable-workflows.
    Workflow files may only change via a trusted ref, so the caller files are
    staged but not committed.

Also not included: dockerfile-nonroot (§6.4). Adding USER to an image with
VOLUME [/config, /data] changes volume ownership and needs an actual container
build/run to verify, so it goes in its own change.

tests/Support/TotpTestHelper.php

@@ -5,11 +5,9 @@ declare(strict_types=1);
 namespace App\Tests\Support;
 
 use App\ConfigBag;
-use App\Enum\RemoteUserMode;
 use App\Utilities;
 use DateTimeImmutable;
 use OTPHP\TOTP;
-use PHPUnit\Framework\TestCase;
 use Psr\Cache\CacheItemInterface;
 use Psr\Cache\CacheItemPoolInterface;
 use Psr\Clock\ClockInterface as PsrClockInterface;
@@ -31,10 +29,12 @@ trait TotpTestHelper
     private function frozenClock(): PsrClockInterface
     {
         $time = self::FROZEN_TIME;
-        return new class ($time) implements PsrClockInterface {
+
+        return new class($time) implements PsrClockInterface {
             public function __construct(private string $time)
             {
             }
+
             public function now(): DateTimeImmutable
             {
                 return new DateTimeImmutable($this->time);
@@ -47,6 +47,7 @@ trait TotpTestHelper
     {
         $totp = TOTP::createFromSecret(self::TOTP_SECRET, $this->frozenClock());
         $totp->setLabel('Test-TOTP');
+
         return $totp->getProvisioningUri();
     }
 
@@ -79,6 +80,7 @@ trait TotpTestHelper
     ): ConfigBag {
         $clock = $this->frozenClock();
         $utilities = $this->createUtilities($clock);
+
         return new ConfigBag(
             $utilities,
             $clock,
@@ -107,6 +109,7 @@ trait TotpTestHelper
         $item = $this->createStub(CacheItemInterface::class);
         $item->method('isHit')->willReturn(false);
         $cache->method('getItem')->willReturn($item);
+
         return new Utilities($clock, $cache);
     }
 }