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/ConfigBagTest.php

@@ -18,7 +18,7 @@ final class ConfigBagTest extends TestCase
         $clock = $this->createStub(ClockInterface::class);
         $cache = $this->createStub(CacheItemPoolInterface::class);
 
-        if ($totp !== null) {
+        if (null !== $totp) {
             $item = $this->createStub(CacheItemInterface::class);
             $item->method('isHit')->willReturn(true);
             $item->method('get')->willReturn($totp);
@@ -31,7 +31,7 @@ final class ConfigBagTest extends TestCase
         return new Utilities($clock, $cache);
     }
 
-    public function testGettersWithExplicitValues(): void
+    public function test_getters_with_explicit_values(): void
     {
         $clock = $this->createStub(ClockInterface::class);
         $utilities = $this->createUtilities();
@@ -61,7 +61,7 @@ final class ConfigBagTest extends TestCase
         self::assertSame('Too Many!', $config->tooManyTitle());
     }
 
-    public function testTotpUriFallsBackToUtilitiesWhenEmpty(): void
+    public function test_totp_uri_falls_back_to_utilities_when_empty(): void
     {
         $clock = $this->createStub(ClockInterface::class);
         $utilities = $this->createUtilities('fallback-totp');
@@ -84,7 +84,7 @@ final class ConfigBagTest extends TestCase
         self::assertSame('fallback-totp', $config->totpUri());
     }
 
-    public function testIpTtlFallsBackToNullWhenZero(): void
+    public function test_ip_ttl_falls_back_to_null_when_zero(): void
     {
         $clock = $this->createStub(ClockInterface::class);
         $utilities = $this->createUtilities();
@@ -107,7 +107,7 @@ final class ConfigBagTest extends TestCase
         self::assertNull($config->ipTtl());
     }
 
-    public function testIpTtlFallsBackToNullWhenNull(): void
+    public function test_ip_ttl_falls_back_to_null_when_null(): void
     {
         $clock = $this->createStub(ClockInterface::class);
         $utilities = $this->createUtilities();