feat: Add browse button to ImageSourceNode for local file selection

[CodeWithBehnam]

Summary

• Adds a "Browse" button to the ImageSourceNode that opens the native file picker
• Users can now load images from local storage using the file browser
• The button is always visible at the bottom of the drop zone

Changes

• Add hidden file input element for native file picker dialog
• Draw Browse button in the drop zone area with blue styling
• Handle click events on the button to trigger file selection
• Clean up file input element when node is removed
• Update placeholder text to mention the browse option

Test plan

• Add an ImageSourceNode to the canvas
• Click the "Browse" button - file picker should open
• Select an image file - it should load and display in the node
• Remove the node and add a new one - browse functionality should still work
• Drag and drop still works
• Paste from clipboard still works

Behnam Ebrahimi