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/group.py

@@ -0,0 +1,70 @@
+"""Group model for organizing players and content."""
+from datetime import datetime
+from typing import List, Optional
+
+from app.extensions import db
+
+
+# Association table for many-to-many relationship between groups and content
+group_content = db.Table('group_content',
+    db.Column('group_id', db.Integer, db.ForeignKey('group.id'), primary_key=True),
+    db.Column('content_id', db.Integer, db.ForeignKey('content.id'), primary_key=True)
+)
+
+
+class Group(db.Model):
+    """Group model for organizing players with shared content.
+    
+    Attributes:
+        id: Primary key
+        name: Unique group name
+        description: Optional group description
+        created_at: Group creation timestamp
+        updated_at: Last modification timestamp
+    """
+    __tablename__ = 'group'
+    
+    id = db.Column(db.Integer, primary_key=True)
+    name = db.Column(db.String(100), nullable=False, unique=True, index=True)
+    description = db.Column(db.Text, nullable=True)
+    created_at = db.Column(db.DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = db.Column(db.DateTime, default=datetime.utcnow, 
+                          onupdate=datetime.utcnow, nullable=False)
+    
+    # Relationships
+    players = db.relationship('Player', back_populates='group', lazy='dynamic')
+    contents = db.relationship('Content', secondary=group_content, 
+                              back_populates='groups', lazy='dynamic')
+    
+    def __repr__(self) -> str:
+        """String representation of Group."""
+        return f'<Group {self.name} (ID={self.id})>'
+    
+    @property
+    def player_count(self) -> int:
+        """Get number of players in this group."""
+        return self.players.count()
+    
+    @property
+    def content_count(self) -> int:
+        """Get number of content items in this group."""
+        return self.contents.count()
+    
+    def add_player(self, player) -> None:
+        """Add a player to this group.
+        
+        Args:
+            player: Player instance to add
+        """
+        player.group_id = self.id
+        self.updated_at = datetime.utcnow()
+    
+    def remove_player(self, player) -> None:
+        """Remove a player from this group.
+        
+        Args:
+            player: Player instance to remove
+        """
+        if player.group_id == self.id:
+            player.group_id = None
+            self.updated_at = datetime.utcnow()