fix(desktop): restore primary workbench ownership

[Whiteks1]

Summary

• introduce a workbench-priority layout mode for the desktop renderer
• collapse the support lane earlier for workbench-heavy surfaces on common laptop widths
• collapse internal two-column rails earlier so Runs, Compare, Candidates, Run Detail, and Paper Ops stop squeezing the active surface

Issue

• Closes desktop(ui): collapse empty panes and restore primary workbench ownership #342

Validation

• node --check desktop/renderer/app.js
• npm install --include=dev in the clean worktree
• npm run smoke:fallback
• npm run smoke:real-path

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