[novykh]

Summary

• Apply the Sage theme roles across layout surfaces and controls in both themes.
• Refine shared inputs, buttons, tabs, table sizing and actions, and scrollbar styling.
• Give menus and selects two selection treatments. Use a left marker for navigation and a neutral check or checkbox for value pickers. Align the scrollbar with the menu edge.
• Add and update stories and component tests for the shared behavior.

This follows up on #650 and starts from its squash merge on master.

Verification

• yarn lint
• 87 focused Menu and Select tests passed