design(home): refine the full-width testimonials section

[francozeta]

Context

The testimonials section needs to become a full-width editorial transition while retaining the existing Paper shader and Kocteau's quiet visual language.

Scope

• Make the section span the viewport cleanly while its content remains aligned with the page grid.
• Keep the upper transition in the body surface color.
• Introduce a restrained monochromatic lower surface using a distinct shader palette.
• Preserve profile credit, outbound tweet links, automatic rotation, click-to-advance behavior, reduced motion, and fixed minimum height.
• Refine spacing, typography, contrast, and mobile composition.
• Keep WebGL deferred until near the viewport and retain a static fallback.

Acceptance criteria

• No horizontal overflow at any supported viewport.
• Shader and content feel like one section, not a decorative strip.
• Text remains readable across animation states.
• Mobile and tablet preserve hierarchy.
• The section does not add blocking client work to the initial landing render.