feat: Implement module permissions system with database-driven access control

- Added `users_permissions` table for managing user permissions.
- Created `PermissionRepository` for handling permission logic.
- Refactored `controls\Users::permissions()` to utilize the new database structure.
- Introduced AJAX endpoint for saving user permissions.
- Enhanced user management UI with permission checkboxes.
- Added vacation management template for handling employee absences.
- Implemented tests for `PermissionRepository`.

.serena/memories/style_conventions.md

@@ -0,0 +1,18 @@
+# Code Style & Conventions
+
+## PHP
+- PHP 7.4 compatibility required
+- New controllers: `Controllers\{Module}Controller` with camelCase methods
+- New domain: `Domain\{Module}\{Name}Repository` with constructor-injected $mdb
+- Legacy: `controls\{Module}` and `factory\{Module}` with snake_case
+- Templates via `\Tpl::view('module/template', $data_array)`
+- XSS protection via `\Tpl::secureHTML()`
+- UI language: Polish
+
+## File Naming
+- New: `ClassName.php`
+- Legacy: `class.ClassName.php`
+
+## Spacing Style (from existing code)
+- Spaces inside brackets: `$arr[ 'key' ]`, `func( $arg )`
+- Allman-ish brace style with opening brace on same line