Make editor toolbar sticky when scrolling

Problem Statement

Following the recent improvement where the editor expands based on content length (removing the internal scroll), users editing long content face a usability issue: when working at the bottom of lengthy content, they must scroll all the way back to the top to access the editor toolbar.

This creates friction in the editing workflow, particularly for:

• Long documentation pages
• Detailed issue descriptions
• Extensive merge request descriptions
• Wiki pages with substantial content

Current state
CleanShot 2025-08-27 at 15.40.09.mp4

Current Behavior

1. Editor expands to show full content (no internal scroll)
2. Editor toolbar remains fixed at the top of the editor
3. When editing content at the bottom of a long document, users must:
   • Scroll up to access formatting options
   • Lose their place in the document
   • Scroll back down to continue editing

Proposed Solution

Implement a sticky positioning for the editor toolbar that remains visible and accessible as users scroll through the content.

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Feedback from 1:1 sessions with @jmandell