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/Module/Contracts/SessionProvider.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace MintyPHP\App\Module\Contracts;
+
+use MintyPHP\App\AppContainer;
+
+/**
+ * Populates module-specific session data after login and cleans up on logout.
+ *
+ * Called from the login flow after successful authentication. When a module is
+ * deactivated, its provider is not called — session keys are simply not set.
+ */
+interface SessionProvider
+{
+    /**
+     * Populate session keys with module-specific data after successful login.
+     *
+     * @param array<string, mixed> $user The authenticated user record
+     */
+    public function populate(array $user, AppContainer $container): void;
+
+    /**
+     * Remove session keys owned by this module (called on logout).
+     */
+    public function clear(AppContainer $container): void;
+}