fix(gantt): properly cleanup mouseup event and destroy component

[Ander1404]

🐛 Problem

The Gantt component was attaching global listeners (document.addEventListener('mouseup')) using anonymous functions, making it impossible to remove them when the component was destroyed or re-created.

This caused:

• Accumulation of listeners over time
• Unpredictable behavior (drag getting stuck, events firing multiple times)
• Memory leaks
• Blank pages in some cases (SPA)

✅ Solution

• Added a destroy() method to properly clean up:
• Event listeners
• DOM elements (container & SVG)
• CSS classes
• Refactored mouseup handling:
• Used a referenced handler (this.on_mouse_up)
• Explicit removal of the listener via removeEventListener
• Centralized cleanup in cleanup_bar_events

🧪 Impact / Outcome

• Correct lifecycle management of the Gantt component
• Memory leaks fixed
• Stable behavior during drag/resize
• Component can now safely be reset or destroyed

🔍 Notes

• No visual changes
• No breaking changes
• Internal improvement for stability and maintainability