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>

core/Repository/Content/PageRepository.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace MintyPHP\Repository\Content;
+
+use MintyPHP\DB;
+
+/** Looks up CMS page metadata by slug. */
+class PageRepository
+{
+    private static function unwrap(?array $row): ?array
+    {
+        if (!$row) {
+            return null;
+        }
+        return $row['pages'] ?? $row;
+    }
+
+    public static function findBySlug(string $slug): ?array
+    {
+        $row = DB::selectOne(
+            'select id, uuid, slug, created_by, modified_by, created, modified from pages where slug = ? limit 1',
+            $slug
+        );
+        return self::unwrap($row);
+    }
+}