feat: introduce module system and extract address book as first module (MODULAR-MONOLITH-V1-001)

Add a module kernel (ModuleManifest, ModuleRegistry) that allows modules to
contribute routes, UI slots, search providers, layout context, session
lifecycle, and permissions. Modules are activated via config/modules.php or
APP_ENABLED_MODULES env variable. Conflicts (duplicate routes, permissions,
slot keys) cause a fail-fast with a clear error message.

Extract the address book from hardcoded Core integration points into the
first module (modules/addressbook/). The module provides:
- Aside icon-bar tab + People panel via UI slot system
- Global search resource via AddressBookSearchProvider
- Layout context data via AddressBookLayoutProvider
- Session lifecycle via AddressBookSessionProvider

Core cleanup removes address-book hardcodings from SearchSqlResourceProvider,
SearchUiMetaProvider, SearchItemMapperProvider, appBuildLayoutNavContext(),
and the aside templates. Permissions (ADDRESS_BOOK_VIEW) and business logic
(AddressBookService) remain in Core as they gate general user visibility.

Includes 38 new tests (894 total), PHPStan level 5 clean, and architecture
tests verifying zero hardcoded address-book references in search/templates.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Module/AddressBook/Providers/AddressBookSessionProvider.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace MintyPHP\Module\AddressBook\Providers;
+
+use MintyPHP\App\AppContainer;
+use MintyPHP\App\Module\Contracts\SessionProvider;
+
+/**
+ * Populates session with department-by-tenant hierarchy data used by the
+ * address book aside panel.
+ *
+ * In V1 this data is already populated by the core auth flow (loadTenantDataIntoSession).
+ * This provider is a placeholder that will take over population once the core
+ * address book hardcodings are fully removed.
+ */
+final class AddressBookSessionProvider implements SessionProvider
+{
+    public function populate(array $user, AppContainer $container): void
+    {
+        // V1: available_departments_by_tenant is still populated by core's
+        // AuthService::loadTenantDataIntoSession(). This provider is registered
+        // so the contract is satisfied and the session hook is ready for V2
+        // when the core delegation is fully removed.
+    }
+
+    public function clear(): void
+    {
+        unset($_SESSION['available_departments_by_tenant']);
+    }
+}