Navigation: consolidate Factory and Explore into workspaces

[ApocDev]

Outcome

Reduce the number of peer concepts in global navigation while preserving every existing capability and deep link.

Scope

• Make Factory, Coherence, and What-if modes of one Factory workspace.
• Make Browse and Deps modes of one Explore workspace.
• Keep the existing route URLs valid and directly linkable.
• Show the active workspace correctly for every child route in desktop and mobile navigation.
• Add a consistent in-workspace mode switcher to the relevant pages.
• Update command palette/navigation tests, documentation, and responsive E2E coverage.

Part of #35.