Visor: center wide-screen content with full-width surfaces

[lannbot]

Summary

• Center drawer, strip, action-bar and confirmation content in an approximately 720px column on wide views.
• Keep surface backgrounds and horizontal borders, including section separators, edge-to-edge.
• Preserve existing mobile gutters and drawer height/scroll behavior.
• CSS-only change; no new markup, dependencies or fixed-geometry tests.

Verification

• Astra review completed.
• CARGO_TARGET_DIR=target just check, just test, and just e2e passed; 29 browser scenarios.
• Real Chromium screenshots and geometry probes at 1440x1000, 1920x1080 and 390x844 covered app list, settings, app info and confirmation.
• Confirmed centered content and full-width surface/border boxes, with existing mobile gutters retained.

Automerge will be armed.