perf(startup): lazy-load ABCJS library to reduce startup blocking

[parthdagia05]

Summary

Closes #5998

This PR implements Phase 4C of the startup performance optimization plan.

The ABCJS library (lib/abc.min.js, ~552KB) was previously loaded during application startup via a <script defer> tag in index.html.

However, ABCJS is only required when users perform ABC-related operations such as:

• Importing ABC notation
• Rendering ABC notation
• Certain AI widget operations

Loading the library during startup caused unnecessary JavaScript parsing and increased Total Blocking Time.

Changes

• Removed the <script defer src="lib/abc.min.js"> tag from index.html
• Implemented a dynamic loader to load the library only when needed
• Ensured ABCJS is loaded before any code paths that use the ABCJS global

Before

ABCJS was loaded and parsed during startup regardless of user interaction.

After

ABCJS loads dynamically only when ABC functionality is triggered.

Impact

• ~552KB JavaScript removed from startup parsing
• Reduced Total Blocking Time
• Improved First Contentful Paint and Speed Index

Risk

Low risk.

ABCJS is only used in user-triggered flows and does not affect core runtime logic.

All functionality related to ABC import and notation rendering continues to work as expected.

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PR Category

• Bug Fix
• Feature
• Performance
• Tests
• Documentation
• Performance

[github-actions]

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

[github-actions]

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

[github-actions]

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

[parthdagia05]

@walterbender can you review PR

[walterbender]

Why do we need multiple copies of EnsureABCJS

[parthdagia05]

@walterbender
Thanks for pointing that out. I introduced ensureABCJS in multiple files to guarantee the library was loaded before use, but that results in duplicated logic. I'll refactor this into a shared utility so all modules use a single loader.

[parthdagia05]

this PR still needs changes.

[github-actions]

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

Failed Tests:

activity_listeners.test.js
GraphicsBlocks.test.js

[github-actions]

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

Failed Tests:

GraphicsBlocks.test.js

[github-actions]

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

Failed Tests:

GraphicsBlocks.test.js

[parthdagia05]

@walterbender this PR is now ready to review, happy for further changes if needed.