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/BookmarksModuleIsolationContractTest.php

@@ -42,7 +42,7 @@ final class BookmarksModuleIsolationContractTest extends TestCase
     {
         $root = dirname(__DIR__, 2);
         self::assertDirectoryDoesNotExist(
-            $root . '/lib/Service/Bookmark',
+            $root . '/core/Service/Bookmark',
             'Bookmark service classes should live in modules/bookmarks/lib, not in Core lib/Service'
         );
     }
@@ -50,7 +50,7 @@ final class BookmarksModuleIsolationContractTest extends TestCase
     public function testCoreNoLongerContainsBookmarkRepositoryFiles(): void
     {
         $root = dirname(__DIR__, 2);
-        $repoDir = $root . '/lib/Repository/User';
+        $repoDir = $root . '/core/Repository/User';
         if (!is_dir($repoDir)) {
             self::addToAssertionCount(1);
             return;
@@ -61,7 +61,7 @@ final class BookmarksModuleIsolationContractTest extends TestCase
         self::assertSame(
             [],
             array_values($bookmarkFiles),
-            'Core lib/Repository/User/ still contains Bookmark files: ' . implode(', ', $bookmarkFiles)
+            'Core core/Repository/User/ still contains Bookmark files: ' . implode(', ', $bookmarkFiles)
         );
     }
 
@@ -69,14 +69,14 @@ final class BookmarksModuleIsolationContractTest extends TestCase
     {
         $root = dirname(__DIR__, 2);
         self::assertFileDoesNotExist(
-            $root . '/lib/Support/BookmarkUrlNormalizer.php',
+            $root . '/core/Support/BookmarkUrlNormalizer.php',
             'BookmarkUrlNormalizer should live in modules/bookmarks/lib, not in Core lib/Support'
         );
     }
 
     public function testCoreAuthLifecycleHasNoLegacyBookmarkSessionKeyWrites(): void
     {
-        $file = dirname(__DIR__, 2) . '/lib/Service/Auth/AuthSessionTenantContextService.php';
+        $file = dirname(__DIR__, 2) . '/core/Service/Auth/AuthSessionTenantContextService.php';
         $content = file_get_contents($file);
         self::assertIsString($content);
         self::assertStringNotContainsString('user_bookmarks', $content);