Add models and utils with type hints and optimizations

Models (6 + 1 association table):
- User: Authentication with bcrypt, admin role check, last_login tracking
- Player: Digital signage devices with auth codes, status tracking, online detection
- Group: Player/content organization with statistics properties
- Content: Media files with type detection, file size helpers, position ordering
- ServerLog: Audit trail with class methods for logging levels
- PlayerFeedback: Player status updates with error tracking
- group_content: Many-to-many association table for groups and content

Model improvements:
- Added type hints to all methods and properties
- Added database indexes on frequently queried columns (username, auth_code, group_id, player_id, position, level, timestamp, status)
- Added comprehensive docstrings
- Added helper properties (is_online, is_admin, file_size_mb, etc.)
- Added relationship back_populates for bidirectional navigation
- Added timestamps (created_at, updated_at, last_seen, uploaded_at)

Utils (4 modules):
- logger.py: Logging utility with level-based functions (info, warning, error)
- uploads.py: File upload handling with progress tracking, video optimization
- group_player_management.py: Player/group status tracking and bulk operations
- pptx_converter.py: PowerPoint to PDF conversion using LibreOffice

Utils improvements:
- Full type hints on all functions
- Comprehensive error handling
- Progress tracking for long-running operations
- Video optimization (H.264, 30fps, max 1080p, 8Mbps)
- Helper functions for time formatting and statistics
- Proper logging of all operations

Performance optimizations:
- Database indexes on all foreign keys and frequently filtered columns
- Lazy loading for relationships where appropriate
- Efficient queries with proper ordering
- Helper properties to avoid repeated calculations

Ready for template migration and testing

app/utils/logger.py

@@ -0,0 +1,78 @@
+"""Logging utility for tracking system events."""
+from typing import Optional
+from datetime import datetime, timedelta
+
+from app.extensions import db
+from app.models.server_log import ServerLog
+
+
+def log_action(level: str, message: str) -> None:
+    """Log an action to the database with specified level.
+    
+    Args:
+        level: Log level (info, warning, error)
+        message: Log message content
+    """
+    try:
+        new_log = ServerLog(level=level, message=message)
+        db.session.add(new_log)
+        db.session.commit()
+        print(f"[{level.upper()}] {message}")
+    except Exception as e:
+        print(f"Error logging action: {e}")
+        db.session.rollback()
+
+
+def get_recent_logs(limit: int = 20, level: Optional[str] = None) -> list:
+    """Get the most recent log entries.
+    
+    Args:
+        limit: Maximum number of logs to return
+        level: Optional filter by log level
+        
+    Returns:
+        List of ServerLog instances
+    """
+    query = ServerLog.query
+    
+    if level:
+        query = query.filter_by(level=level)
+    
+    return query.order_by(ServerLog.timestamp.desc()).limit(limit).all()
+
+
+def clear_old_logs(days: int = 30) -> int:
+    """Delete logs older than specified days.
+    
+    Args:
+        days: Number of days to keep
+        
+    Returns:
+        Number of logs deleted
+    """
+    try:
+        cutoff_date = datetime.utcnow() - timedelta(days=days)
+        deleted = ServerLog.query.filter(ServerLog.timestamp < cutoff_date).delete()
+        db.session.commit()
+        log_action('info', f'Deleted {deleted} old log entries (older than {days} days)')
+        return deleted
+    except Exception as e:
+        db.session.rollback()
+        print(f"Error clearing old logs: {e}")
+        return 0
+
+
+# Convenience functions for specific log levels
+def log_info(message: str) -> None:
+    """Log an info level message."""
+    log_action('info', message)
+
+
+def log_warning(message: str) -> None:
+    """Log a warning level message."""
+    log_action('warning', message)
+
+
+def log_error(message: str) -> None:
+    """Log an error level message."""
+    log_action('error', message)