bug: keep desktop context menus above scrollbar overlays #171

Summary

Project context menus can appear visually beneath overlay scrollbars, making entries partially obscured and hard to use.

Reproduction Steps

1. Open desktop app and trigger context menus in scrollable UI regions.
2. Move pointer near right/bottom edges where overlay scrollbars are visible.
3. Observe menu rendering relative to scrollbar overlay.

Expected Behaviour

Context menus appear above chrome and avoid scrollbar overlay regions.

Actual Behaviour

Menus/submenus can render under scrollbar overlays.

Evidence

• Screenshot/log: pending (screenshot capture closes context menu)
• Notes: issue observed across multiple context menu entry points.

Scope Check

• Affected paths: apps/desktop/src/components/Editor/ContextMenu/ContextMenu.css, apps/desktop/src/components/Editor/ContextMenu/ContextMenu.tsx, apps/desktop/src/components/Editor/ContextMenu/Submenu.tsx
• Affected platforms: Linux/macOS/Windows
• Regression?: unknown

Resolution Notes

• Fix summary: Initial layering and edge-clamping adjustments improved behaviour but did not fully resolve occlusion in this environment. A later environment-specific attempt (GTK_OVERLAY_SCROLLING=0 plus larger gutter) was reverted at user request.
• Commit(s): a588157 (partial), aca9159 (revert of environment-specific attempt)
• Commit footer target: Resolves #XX
• PR/branch: fix/bug-sweep-2026-02-11
• Test(s): pnpm --filter @liminal-notes/desktop lint (pass)
• Follow-ups: unresolved; requires a different approach for this runtime (likely non-overlay scrollbar strategy or environment-specific window/webview settings).

Imported from triage entry BUG-20260211-13.