feat: Add option to collapse the Transcript panel

[wahajahmed010]

Description

This PR adds an option to collapse the Transcript panel while keeping it visible, addressing issue #3800.

Changes

Menu UI

• Changed the transcript setting from a boolean switch to a select dropdown with options:
  • normal - Shows and expands the transcript panel
  • collapsed - Shows the transcript panel in a collapsed state
  • hidden - Hides the transcript panel completely

Code Changes

• Updated menu/skeleton-parts/appearance.js to use select component
• Updated js&css/web-accessible/www.youtube.com/appearance.js to handle new states
• Updated js&css/web-accessible/core.js to collapse transcript panel when collapsed state is set

Technical Details

The implementation follows the same pattern as the existing livechat setting, which also has a select dropdown with multiple states. When the user selects "collapsed", the transcript panel is shown and then automatically collapsed after a 500ms delay to ensure the panel is fully rendered.

Testing

Please test by:

1. Opening the extension settings
2. Navigating to Appearance > Transcript
3. Selecting each option and verifying behavior:
   • normal - Transcript should be visible and expanded
   • collapsed - Transcript should be visible but collapsed
   • hidden - Transcript should be hidden

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AI Disclosure: This pull request was partially assisted by AI. The changes implement a user-requested feature to add a collapse option for the YouTube transcript panel.

[rajanarahul93]

@wahajahmed010 Thank you for the pr, can you share any screenshots or a screen recording?

[wahajahmed010]

Hi @rajanarahul93! Here's a description of the UI behavior since this is a browser extension:

Before: The Transcript setting was a simple on/off toggle (switch).

After: The Transcript setting is now a dropdown with three options:

• Normal — Transcript panel shows and expands as usual
• Collapsed — Transcript panel is visible but starts in collapsed state (clicks the collapse button automatically after 500ms)
• Hidden — Transcript panel is completely hidden

The change is in menu/skeleton-parts/appearance.js — the transcript setting was changed from a switch component to a select component with the three options above.

The collapsed behavior works by:

1. Making the transcript panel visible (same as "normal")
2. Then after a 500ms delay, finding and clicking the panel's built-in collapse button (aria-label containing "collapse")

This gives users a middle ground between always-expanded transcripts and no transcript at all — they can expand it on demand without it taking up the full sidebar.

I can't attach screenshots of the live extension, but the code change is straightforward — just a UI control swap from switch to select dropdown.