Fix mobile workspace sidebar drawer default state

[Cataldir]

Summary

• keeps the workspace sidebar closed by default on mobile and tablet while remaining visible on desktop
• preserves explicit sidebar open/close toggle behavior across breakpoints
• adds route-shell coverage for mobile/tablet drawer state, desktop visibility, and overflow safety

Validation

• pnpm --dir frontend typecheck
• pnpm --dir frontend lint
• pnpm --dir frontend exec playwright test e2e/route-shells.spec.ts
• git diff --check