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/models/content.py

@@ -0,0 +1,64 @@
+"""Content model for media files."""
+from datetime import datetime
+from typing import Optional, List
+
+from app.extensions import db
+from app.models.group import group_content
+
+
+class Content(db.Model):
+    """Content model representing media files for display.
+    
+    Attributes:
+        id: Primary key
+        filename: Original filename
+        content_type: Type of content (image, video, pdf, presentation, other)
+        duration: Display duration in seconds
+        file_size: File size in bytes
+        description: Optional content description
+        position: Display order position
+        uploaded_at: Upload timestamp
+    """
+    __tablename__ = 'content'
+    
+    id = db.Column(db.Integer, primary_key=True)
+    filename = db.Column(db.String(255), nullable=False, index=True)
+    content_type = db.Column(db.String(50), nullable=False, index=True)
+    duration = db.Column(db.Integer, default=10, nullable=True)
+    file_size = db.Column(db.BigInteger, nullable=True)
+    description = db.Column(db.Text, nullable=True)
+    position = db.Column(db.Integer, default=0, index=True)
+    uploaded_at = db.Column(db.DateTime, default=datetime.utcnow, 
+                           nullable=False, index=True)
+    
+    # Relationships
+    groups = db.relationship('Group', secondary=group_content, 
+                            back_populates='contents', lazy='dynamic')
+    
+    def __repr__(self) -> str:
+        """String representation of Content."""
+        return f'<Content {self.filename} (Type={self.content_type})>'
+    
+    @property
+    def file_size_mb(self) -> float:
+        """Get file size in megabytes."""
+        if self.file_size:
+            return round(self.file_size / (1024 * 1024), 2)
+        return 0.0
+    
+    @property
+    def group_count(self) -> int:
+        """Get number of groups containing this content."""
+        return self.groups.count()
+    
+    def is_image(self) -> bool:
+        """Check if content is an image."""
+        return self.content_type == 'image'
+    
+    def is_video(self) -> bool:
+        """Check if content is a video."""
+        return self.content_type == 'video'
+    
+    def is_pdf(self) -> bool:
+        """Check if content is a PDF."""
+        return self.content_type == 'pdf'