Fix TypeError when creating a new project from Planet interface (#6185)

[gourijain029-del]

Fixes #6185

Description

This PR fixes a runtime error that appeared when clicking the "New Project" ("+") button in the Planet interface.

The bug occurred because _loadStart() inside js/activity.js was previously refactored and renamed to justLoadStart(), however the corresponding call sequence in js/planetInterface.js hadn't been updated to match the new method name yet.

Expected Behavior

Clicking the "New Project" button inside the Planet interface will now start a blank new project smoothly without throwing a TypeError in the console.

Changes Made

• Replaced this.activity._loadStart() with this.activity.justLoadStart() inside js/planetInterface.js.
• Updated Jest unit tests in js/__tests__/planetInterface.test.js so that they mock and verify justLoadStart instead of the deprecated _loadStart function.

PR Category

• Bug Fix
• Feature
• Performance
• Tests
• Documentation

Checklist

• I have read and followed the project's code of conduct.
• I have tested the change locally.
• I have verified all existing tests are still passing.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[Ashutoshx7]

@gourijain029-del you forgot to add category checks

[gourijain029-del]

@gourijain029-del you forgot to add category checks

added category checks

[Ashutoshx7]

@gourijain029-del hy take a look i drop some comments
remove unrelated changes

[github-actions]

❌ Some Jest tests failed. Please check the logs and fix the issues before merging.

Failed Tests:

GraphicsBlocks.test.js

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.