Landing page: adopt robocurve.org's clean style; quickstart: catch up with README (LLM policies, real-rig setup)

[jeqcho]

Two follow-ups to the Docusaurus migration (#149):

1. https://inspectrobots.org/guide/quickstart/ predates the README rewrite (docs(readme): add logo, drop redundant concept section, trim asides #147). It is missing the real-rig setup wizard flow, driving the robot with an LLM (--policy agent), CaP-X code-as-policy, --sim, and the view/video commands.
2. The landing page still uses the heavy gradient/shadow look. Restyle it to match robocurve.org's clean editorial style: cream page, Space Grotesk type, near-black headings, white hairline cards, teal as accent only.

Plan: plans/0025-landing-style-and-quickstart-refresh.md.