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/Unit/UtilitiesTest.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace App\Tests\Unit;
 
 use App\Utilities;
+use DateTimeImmutable;
 use PHPUnit\Framework\TestCase;
 use Psr\Clock\ClockInterface;
 use Symfony\Component\Cache\Adapter\ArrayAdapter;
@@ -15,10 +16,11 @@ final class UtilitiesTest extends TestCase
     {
         $pool ??= new ArrayAdapter();
         $clock ??= $this->createStub(ClockInterface::class);
+
         return new Utilities($clock, $pool);
     }
 
-    public function testLoadTotpReturnsCachedValueWhenPresent(): void
+    public function test_load_totp_returns_cached_value_when_present(): void
     {
         $pool = new ArrayAdapter();
         $item = $pool->getItem('totp');
@@ -32,7 +34,7 @@ final class UtilitiesTest extends TestCase
         self::assertSame('otpauth://totp/cached?secret=ABCDEFGH', $result);
     }
 
-    public function testLoadTotpGeneratesAndStoresWhenMissing(): void
+    public function test_load_totp_generates_and_stores_when_missing(): void
     {
         $pool = new ArrayAdapter();
         $utilities = $this->makeUtilities($pool);
@@ -48,7 +50,7 @@ final class UtilitiesTest extends TestCase
         self::assertSame($result, $cached->get());
     }
 
-    public function testLoadTotpSetsFarFutureExpiry(): void
+    public function test_load_totp_sets_far_future_expiry(): void
     {
         $pool = new ArrayAdapter();
         $utilities = $this->makeUtilities($pool);
@@ -58,10 +60,10 @@ final class UtilitiesTest extends TestCase
         $cached = $pool->getItem('totp');
         $expiry = $cached->getMetadata()['expiry'];
         // 2999-12-31 is well in the future, far beyond any reasonable test timestamp
-        self::assertGreaterThan((new \DateTimeImmutable('+10 years'))->getTimestamp(), (int) $expiry);
+        self::assertGreaterThan((new DateTimeImmutable('+10 years'))->getTimestamp(), (int) $expiry);
     }
 
-    public function testLoadTotpIsIdempotentAfterGeneration(): void
+    public function test_load_totp_is_idempotent_after_generation(): void
     {
         $pool = new ArrayAdapter();
         $utilities = $this->makeUtilities($pool);