Fix mobile web workspace explorer overlay

[ayhanmalkoc]

Fixes #777

Summary

• Treat workspace md breakpoints as compact so pane-heavy workspace layouts use mobile overlay behavior on narrow mobile web viewports.
• Keep the workspace explorer sidebar, animation provider, and workspace screen on the same compact-layout decision.
• Add regression coverage for app-wide vs workspace-specific compact breakpoint helpers.

Root Cause

Mobile web viewports can resolve to the md breakpoint. The workspace screen still showed the mobile-style explorer toggle, but the explorer sidebar used the desktop panel state/rendering path, leaving the Changes/Files panel pinned beside the chat instead of behaving as a right-side overlay.

Validation

• npm run format
• npx vitest run src/constants/layout.test.ts --bail=1
• npm run typecheck
• npm run lint