Fix - Canvas item selection + move + Cut (Split) a timeline item

[parth0025]

Task 1 : Canvas item selection + move

• Add real-time position clamping during object:moving event
• Add final boundary check on object:moved event
• Clamp handles rotated and scaled objects correctly
• Smooth clamping prevents jitter during drag

Task 2: Cut (Split) a timeline item

• Add splitImageElement() method to split image clips while preserving fabric objects
• Add splitAudioElement() method to split audio with proper offset handling
• Add splitVideoElement() method to split video with offset and thumbnail management
• All split methods properly update time frames and maintain playback continuity
• Integration with MobX state management and history tracking