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/App/AppContainer.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace MintyPHP\App;
+
+use RuntimeException;
+
+// Minimal DI container: factories are registered with set() and resolved lazily on first get().
+// Each service is instantiated at most once — get() returns the same instance on every call.
+final class AppContainer
+{
+    /** @var array<string, callable(self): mixed> */
+    private array $bindings = [];
+
+    /** @var array<string, mixed> */
+    private array $instances = [];
+
+    private bool $protectExistingBindings = false;
+
+    public function set(string $id, callable $factory): void
+    {
+        if ($this->protectExistingBindings && $this->has($id)) {
+            throw new RuntimeException('Refusing to overwrite existing service binding: ' . $id);
+        }
+        $this->bindings[$id] = $factory;
+    }
+
+    public function has(string $id): bool
+    {
+        return array_key_exists($id, $this->instances) || array_key_exists($id, $this->bindings);
+    }
+
+    public function get(string $id): mixed
+    {
+        if (array_key_exists($id, $this->instances)) {
+            return $this->instances[$id];
+        }
+
+        if (!array_key_exists($id, $this->bindings)) {
+            throw new RuntimeException('Service not bound: ' . $id);
+        }
+
+        // Resolve, cache, and return — factory receives the container for its own dependencies.
+        $this->instances[$id] = ($this->bindings[$id])($this);
+        return $this->instances[$id];
+    }
+
+    /**
+     * Freeze existing bindings/instances: any later overwrite attempt throws.
+     */
+    public function protectExistingBindings(): void
+    {
+        $this->protectExistingBindings = true;
+    }
+}