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/Domain/Taxonomy/SupportsStringTaxonomy.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace MintyPHP\Domain\Taxonomy;
+
+trait SupportsStringTaxonomy
+{
+    /**
+     * @return list<string>
+     */
+    public static function values(): array
+    {
+        return array_map(
+            static fn (self $case): string => $case->value,
+            self::cases()
+        );
+    }
+
+    public static function tryNormalize(string $value): ?self
+    {
+        $value = strtolower(trim($value));
+        if ($value === '') {
+            return null;
+        }
+
+        foreach (self::cases() as $case) {
+            if (strtolower($case->value) === $value) {
+                return $case;
+            }
+        }
+
+        return null;
+    }
+
+    public static function normalizeOr(string $value, self $fallback): self
+    {
+        return self::tryNormalize($value) ?? $fallback;
+    }
+}