Increase editor bottom reserved space to 150px

[yasyuk]

Summary

• Increased J.Size.lastBlock from 80 to 150 in src/json/size.ts — this is the minimum height floor for the dynamically-calculated bottom spacer
• Updated the .blockLast CSS height from 44px to 150px in src/scss/component/editor.scss for consistency

Test plan

• Open any object in the editor and verify there is more reserved space at the bottom
• Verify the "Start a discussion" button still appears correctly above the spacer

🤖 Generated with Claude Code

[github-actions]

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