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/Dockerfile

@@ -12,7 +12,8 @@ LABEL org.opencontainers.image.description="PicPeak Backend Service"
 LABEL org.opencontainers.image.licenses="MIT"
 
 # Upgrade npm to fix glob CVE-2025-64756 vulnerability
-RUN npm install -g npm@latest
+# Pin to npm 10.x which supports --omit=dev flag
+RUN npm install -g npm@10
 
 WORKDIR /app
 
@@ -34,7 +35,8 @@ WORKDIR /app
 RUN apk upgrade --no-cache
 
 # Upgrade npm to fix glob CVE-2025-64756 vulnerability
-RUN npm install -g npm@latest
+# Pin to npm 10.x which supports --omit=dev flag
+RUN npm install -g npm@10
 
 # Install dumb-init for proper signal handling and postgresql-client for database checks
 RUN apk add --no-cache dumb-init postgresql-client
@@ -46,8 +48,8 @@ RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001
 COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
 COPY --chown=nodejs:nodejs . .
 
-# Make wait script executable
-RUN chmod +x wait-for-db.sh
+# Ensure all source files are readable and wait script is executable
+RUN chmod -R a+r /app && chmod +x wait-for-db.sh
 
 # Create necessary directories
 RUN mkdir -p storage/events/active storage/events/archived storage/thumbnails data logs && \