feat: add multi-administrator support with RBAC and fix backup/restore for S3

## Multi-Administrator System
- Add role-based access control (RBAC) with predefined roles (Super Admin, Admin, Editor, Viewer)
- Add granular permissions system for all admin operations
- Add admin user management page with invite functionality
- Add email invitation system for new administrators
- Add permission middleware protecting all admin routes
- Add PermissionGate component for frontend permission checks
- Track event creator (created_by) for audit purposes

## Backup & Restore Fixes
- Fix S3 backup: endpoint URL handling, manifest loading, field name compatibility
- Fix S3 restore: add list-backups endpoint, transform S3 config from frontend format
- Fix PostgreSQL compatibility: add .returning('id') for insert operations
- Fix disk space check: use df command, handle unknown space gracefully
- Fix dry-run validation to not block on warnings
- Fix req.user → req.admin in restore routes

## Database Migrations
- 054: Add roles table with predefined roles
- 055: Add permissions table
- 056: Add role_permissions junction table
- 057: Add role_id to admin_users
- 058: Add admin_invitations table
- 059: Add admin email templates
- 060: Add created_by to events table

## Other Improvements
- Update .gitignore to exclude planning docs and local backup directory
- Remove SQLite database file from tracking
- Add i18n translations for user management (EN/DE)

backend/src/routes/adminCategories.js

@@ -3,10 +3,11 @@ const { body, validationResult } = require('express-validator');
 const { db, logActivity } = require('../database/db');
 const { formatBoolean } = require('../utils/dbCompat');
 const { adminAuth } = require('../middleware/auth');
+const { requirePermission } = require('../middleware/permissions');
 const router = express.Router();
 
 // Get all global categories
-router.get('/global', adminAuth, async (req, res) => {
+router.get('/global', adminAuth, requirePermission('settings.view'), async (req, res) => {
   try {
     const categories = await db('photo_categories')
       .where('is_global', formatBoolean(true))
@@ -20,7 +21,7 @@ router.get('/global', adminAuth, async (req, res) => {
 });
 
 // Get categories for a specific event (global + event-specific)
-router.get('/event/:eventId', adminAuth, async (req, res) => {
+router.get('/event/:eventId', adminAuth, requirePermission('settings.view'), async (req, res) => {
   try {
     const { eventId } = req.params;
     
@@ -40,7 +41,7 @@ router.get('/event/:eventId', adminAuth, async (req, res) => {
 });
 
 // Create a new category
-router.post('/', adminAuth, [
+router.post('/', adminAuth, requirePermission('settings.edit'), [
   body('name').notEmpty().withMessage('Category name is required'),
   body('slug').optional(),
   body('is_global').optional().isBoolean(),
@@ -104,7 +105,7 @@ router.post('/', adminAuth, [
 });
 
 // Update a category
-router.put('/:id', adminAuth, [
+router.put('/:id', adminAuth, requirePermission('settings.edit'), [
   body('name').notEmpty().withMessage('Category name is required')
 ], async (req, res) => {
   try {
@@ -149,7 +150,7 @@ router.put('/:id', adminAuth, [
 });
 
 // Delete a category
-router.delete('/:id', adminAuth, async (req, res) => {
+router.delete('/:id', adminAuth, requirePermission('settings.edit'), async (req, res) => {
   try {
     const { id } = req.params;