refactor: rename lib/ to core/ for clearer core-module separation

Rename the top-level lib/ directory to core/ so the project root
immediately communicates which code is core platform and which lives
in modules/. PHP namespaces (MintyPHP\*) are unchanged — only the
Composer PSR-4 path mapping moves from lib/ to core/.

Module-internal lib/ directories (modules/*/lib/) are untouched.

Updated across the full stack:
- composer.json PSR-4 mapping
- bootstrap entry points (web/index.php, bin/*, tests/bootstrap.php)
- tooling configs (phpstan.neon, phpunit.xml, php-cs-fixer)
- 26 architecture contract tests
- enforcement-policy, guard-catalog, quality-gates
- all documentation (CLAUDE.md, README, 25 docs/, .agents/skills/)
- bin/qa-extended.sh search paths
- .claude/settings.local.json permission paths

Workflow: .agents/runs/CORE-LIB-RENAME-001/ (Analyst → Planner →
Executor → Code Review (4 findings fixed) → Security Review →
Acceptance Test → Finalizer)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/Architecture/ServiceLayerNoHtmlContractTest.php

@@ -16,7 +16,7 @@ class ServiceLayerNoHtmlContractTest extends TestCase
 
     /** @var list<string> */
     private const EXCLUDED_FILES = [
-        'lib/Service/User/UserAccessPdfService.php',
+        'core/Service/User/UserAccessPdfService.php',
     ];
 
     /**
@@ -27,8 +27,8 @@ class ServiceLayerNoHtmlContractTest extends TestCase
 
     public function testServicesContainNoHtmlTags(): void
     {
-        $violations = $this->findHtmlViolations('lib/Service');
-        $violations = array_merge($violations, $this->findHtmlViolations('lib/Http'));
+        $violations = $this->findHtmlViolations('core/Service');
+        $violations = array_merge($violations, $this->findHtmlViolations('core/Http'));
 
         self::assertSame(
             [],