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/Service/Settings/ThemeConfigGateway.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace MintyPHP\Service\Settings;
+
+class ThemeConfigGateway
+{
+    private const DEFAULT_THEMES = [
+        'light' => 'Light',
+        'dark' => 'Dark',
+    ];
+
+    private ?array $themes = null;
+
+    public function all(): array
+    {
+        if ($this->themes !== null) {
+            return $this->themes;
+        }
+
+        $file = dirname(__DIR__, 3) . '/config/themes.php';
+        if (!is_file($file)) {
+            $this->themes = self::DEFAULT_THEMES;
+            return $this->themes;
+        }
+
+        $loaded = include $file;
+        if (!is_array($loaded)) {
+            $this->themes = self::DEFAULT_THEMES;
+            return $this->themes;
+        }
+
+        $clean = [];
+        foreach ($loaded as $key => $label) {
+            $themeKey = strtolower(trim((string) $key));
+            $themeLabel = trim((string) $label);
+            if ($themeKey === '' || $themeLabel === '') {
+                continue;
+            }
+            $clean[$themeKey] = $themeLabel;
+        }
+
+        // Fall back to defaults if the file returns an empty or invalid list — system must always have themes.
+        $this->themes = $clean ?: self::DEFAULT_THEMES;
+        return $this->themes;
+    }
+}