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/RepositoryInterfaceContractTest.php

@@ -40,7 +40,7 @@ class RepositoryInterfaceContractTest extends TestCase
     private function collectRepositoryPairs(): array
     {
         $root = $this->projectRootPath();
-        $repoDir = $root . '/lib/Repository';
+        $repoDir = $root . '/core/Repository';
 
         $pairs = [];
 
@@ -64,9 +64,9 @@ class RepositoryInterfaceContractTest extends TestCase
                 continue;
             }
 
-            // Derive PSR-4 class name: lib/Repository/Foo/Bar.php → MintyPHP\Repository\Foo\Bar
+            // Derive PSR-4 class name: core/Repository/Foo/Bar.php → MintyPHP\Repository\Foo\Bar
             $relativePath = ltrim(str_replace($root, '', $file->getPathname()), '/');
-            $className = 'MintyPHP\\' . str_replace(['/', '.php'], ['\\', ''], substr($relativePath, strlen('lib/')));
+            $className = 'MintyPHP\\' . str_replace(['/', '.php'], ['\\', ''], substr($relativePath, strlen('core/')));
 
             if (in_array($className, self::EXCLUDED_CLASSES, true)) {
                 continue;