fix(web): new workbench, onboarding, worker page, and theme polish match the mockups (CL-9589)

[TheGreatAxios]

• /new: mockup heading, hint line, plain Start, Workbenches / New breadcrumb; chips removed
• Onboarding: Myra step ends on a ready screen; provider rows get neutral icons
• Worker page: Created/Runs from runs data, real workbenches in the Workbench card
• Settings: IdentityAvatar, ink active nav row, styled Advanced; opaque voice backdrop; Canvas surfaces warmed
• Docs: BETTER_AUTH_BASE_URL in .env.example and local-dev.md

Resolves CL-9589

[linear-code]

CL-9589