[GaganSD]

Summary

• Move the thinking level after context/MCP on the top-right edge when the dashboard is hidden.
• Keep the model below without repeating thinking; remove the old 80-column thinking cutoff.
• Paint diff split dividers and truncation ellipses explicitly to prevent surrounding tool/terminal backgrounds leaking into edit previews.
• Add narrow-screen and diff-background rendering regression coverage.

Validation

• 622 Slate tests pass.
• Slate typecheck and lint pass.
• Synced through the existing local Slate package link for manual testing.
• Awaiting manual approval before merge.